Home » Technical-Screw Jack Frequently Asked Questions
Technical-Screw Jack Frequently Asked Questions
What is axially translating screw jack?
A driven worm shaft acts on an internal worm gear, which in turn drives a lifting screw to extend or retract. As the lifting screw translates through the jack housing, inherent screw rotation is prevented by an attached load, full guidances or mounting structure that is anchored to resist rotation. The lifting screw will move linearly through the housing to push or pull the load.
What is anti-rotation keyed screw jack?
The lifting screw of a translating screw jack must be attached to the load which prevents the lifting screw from rotating. Otherwise, the lifting screw and the load will turn and not translate. A keyed screw jack can prevent lifting screw rotation, which has milled keyway along the length of the lifting screw. A matching key is fastened to the cover of the jack, which will eliminate jack screw rotation. The keyway in the screw causes greater than normal wear on the internal drive worm gear threads, somewhat reducing screw jack lifespan. Note: jtb series and jtd series ball screw jack anti-rotation devices by square protective pipe with square nut.
What is traveling nut rotating screw jack?
A keyed for traveling nut rotating screw jack features a lifting screw keyed to the internal worm gear as a single unit, forcing the lifting screw to rotate, but not translate. A travelling nut, attached to the load, is driven by the rotation of the lifting screw. This type of jack is ideal for applications that cannot accommodate a screw protective tube or that require a flush mount.
What is the difference between an acme screw jack and a ball screw jack?
The acme screw jack uses an acme threaded screw that is completely self-locking, meaning it will hold its position without a brake mechanism or locking systems. Ball screw jack use ball screws and ball nuts to convert rotary motion to linear movement, and require approx. 1/3 the horsepower compared to a acme screw jack. Due to the efficiency of the ball screw, brake mechanism must be used to stop and hold the lifting screw in position. Brake mechanism is also recommended for use on any screw jack if vibration is present.
Why use an acme screw jack and a ball screw jack?
One type of screw jack is usually better suited to the operating conditions. Typically, fast travel speed and frequent cycle times may be more suited to a ball screw jack, particularly as the load approaches the rated capacity of the screw jack. High load at slow travel speed, less frequent cycles and the ability to hold the load in position when the system is at rest may be better suited for an acme screw jack.
How do I operate the screw jack?
Manual operation, motor driven, or both together.
Various of motors / reducer driven such as 3-phase asynchronous motor, helical gear reducer, worm gear reducer, but air motors and hydraulic motors can also be used. Hand wheel or crank handle can be used for manual operation.
Can I use a larger motor than required in specifications?
Yes, the specifications data is a theoretical value, the motor power should be a little larger than required in specifications, but if the motor power is much more larger than required in specifications, it is not recommended. The screw jack or jack system components could be damaged if an large oversize motor is used. Travel limit switches control must be used for each end of travel to stop the motor. If using solid mechanical stops, screw jack components can be subject to shock load conditions and oversize motors can cause catastrophic failure of stops and other components.
How do I stop the screw jack at the travel limits?
Limit switches or other controls must be used to shut off the motor when the screw jack has reached its full extend or retracted position. Solid mechanical stops are not recommended. Their continued use can cause severe damage to the screw jack.
Can different size screw jacks be used in the same system?
Yes, as long as the equal travel length per full turn of worm shaft input. This is sometimes done to accommodate varying load conditions.
What is the screw jack lifting systems efficiency?
Two screw jack lift system efficiency is 95%.
Three screw jack lift system efficiency is 90%.
Four screw jack lift system efficiency is 85%.
Six screw jack lift system efficiency is 80%.
Miter gearbox efficiency is 95-98%.
Single reduction helical gear reducer efficiency is 98%, Double reduction helical gear reducer efficiency is 97%. Worm gear reducer efficiency is horsepower out x 100 / horsepower in.
What is the maximum input speed?
JACTON screw jack can be run at 1500Rpm. A gear motor, helical gear reducer, or a worm gear reducer is used to reduce the input Rpm to the screw jack to provide the required travel speed of the lifting screw. Many JACTON screw jacks can be driven directly by 1500Rpm and 900Rpm 3-phase motors. Electric motors and gear reducers are available mounted directly to many JACTON screw jacks models.
What causes heat build up in the screw jack?
The screw jack is a mechanical gearbox assembly. The friction of the worm and worm gear set, lifting screw and worm gear set, bearings and seals generate heat while the screw jack is operating. The combination of travel, loading, and input speed all affect the temperature rise of the screw jack. JACTON screw jack sizing calculations take these variables into account to insure that you select the right screw jack model for your application.
What is the screw jack load capacity and travel?
This is based on the relationship of the lifting screw diameter and the length. Lifting screws in tension are rated for the full capacity of the screw jack, regardless of length, providing they do not rotate faster than the critical speed. For the lifting screw in compression, capacity is limited by the screw jack's permissible buckling load. The permissible buckling load of a lifting screw is reduced as the lifting screw gets longer. Use the maximum extended lifting screw length when using the permissible buckling load charts to determine screw jack load capacity.
How do I determine the full-extended lifting screw length?
The extended lifting screw length is normally equal to the travel stroke. If screw jack is equipped with bellows boot and stop nut, must be added the bellows boot full retract length and the addition stop nut or special closed height. These must be increased the extended lifting screw length. For inverted screw jack, the thickness of the mounting structure must be included. This total extended lifting screw length should be used when determining the permissible buckling load of the screw jack.
Should the load being positioned be guided?
It is highly recommended that the load be guided, however, it is not necessary. A guided system will provide more column stability and allow longer screw jack travel. Column length is greatly reduced on unguided systems. External load forces common with unguided systems are detrimental to the life and operation of the screw jack.
Can the screw jack withstand side loading or a bending moment?
Yes, but this is not recommended. Consult JACTON if this condition will be present. These types of loads apply greater forces on the screw jack and housing assembly causing premature wear. Guides are highly recommended and should be used to eliminate side and bending loads.
Can the screw jack withstand shock loading?
This is not recommended. Oversized screw jacks are required to handle shock loads. Solid thrust bearings are also available in many screw jack models when constant vibration and shock are present in an application.
What is the difference between upright and inverted screw jack configurations?
The difference between an upright and an inverted screw jack is the location at which the lifting screw exits the jack relative to the jack gearbox. For example, an upright screw jacks lifting screw exits the jack opposite the gearbox. An inverted screw jacks lifting screw exits the jack on the same side as the gearbox. The choice between inverted and upright screw jack is dependent upon the application.
Note: An upright screw jack mounted upside down is still referred to as an upright screw jack.
How is the linear travel speed calculated?
Each screw jack has an inherent number show lifting screw travel per full turn of worm shaft input. The result of the screw jack is equal to the lifting screw pitch divided by worm gear ratio. For example, JT-10T model screw jack, screw pitch 8mm, high worm gear ratio 1/8, the lifting screw travel is 1mm per full turn of worm shaft input. If 900Rpm is applied to the worm shaft, the linear travel speed is 900Rpm multiplied by 1mm/r, equal to 900 millimeter per minute.
Are screw jacks lubricated prior to shipment?
All JACTON screw jacks are lubricated with a synthetic grease extreme pressure #2 grease before leaving the factory. They are grease lubricated prior to shipment.
What electric motors options are available?
Electric motor options vary among product lines. Customers can use AC 3-phase motor, AC single-phase motor, DC motor. Standard voltage of China is 380V/220V, 3-phase, 50Hz, or 220V, single-phase, 50Hz. Customized international voltage motors like America 110V-single phase-60hz, 240V/480V-three phase-60Hz, other voltages 230V/240V-single phase-50hz, 400V/415V/440V-three phase-50hz etc.
Are screw jacks corrosion resistant?
Stainless steel screw jacks are inherently corrosion resistant. All exposed surfaces are stainless steel and aluminum bronze. Most other screw jacks can be modified with special finishes, coatings, and seals.
Can bellow boots be supplied for an screw jack model with inverted screw?
Yes, but allowance must be made in the length of the lifting screw for both the closed height of the boots and structure thickness. Since we can make no provision for attaching a boot on the underside of your structure, we suggest that a circular plate similar to the lifting screw top plate be welded or bolted to the bottom of your structure supporting the screw jack, thereby making it possible to use a standard bellow boots.
Is there backlash between the lifting screw and worm gear?
Yes. This is necessary to allow for sliding or rolling action of the lifting screw through the worm gear. Anti-backlash nut screw jack is available when the backlash needs to be minimized.
How is the lifting screw protected?
Standard translating screw jack is fitted with a lifting screw protective tube that stores the lifting screw when the screw jack is in the closed position. Bellow boots is available and recommended to protect the lifting screw in the extended position. Double bellows boots are required for rotating screw jack with traveling nut.
How do I attach the load to be positioned to the lifting screw?
For translating screw jack, the lifting screw has a standard threaded end that can be used to attach the load, top plate, clevis end, plain end and forked head are also available. For traveling nut rotating screw design, the traveling nut has a flange with mounting holes. The screw jack gearbox has a mounting base and is also available with a clevis mount for double clevis requirements.
Will the lifting screw rotate?
Yes. You need to prevent the lifting screw from rotating to produce linear motion. The lifting screw will not rotate in a multiple screw jack lift system with all the lifting screws attached to the same structure. If rotation of the screw cannot be prevented in the application design, a anti-rotation keyed screw design jack is available. Input torque will increase for keyed jacks and the capacity may be reduced to 25% of rating.
What is the maximum and minimum operating temperature?
Standard JACTON screw jacks are designed to operate at maximum 80 deg.C (185 deg.F) ambient temperature. For higher temperatures, special grease and seals are required, contact JACTON of these special requirements. Minimum minus 20 deg.C (minus 4 deg.F) ambient temperature. For lower temperatures, special grease and seals are required, contact JACTON of these special requirements.
How do I lubricate a screw screw jack?
Use the proper grease. Fill the housing/gearbox by pumping grease into the grease fittings supplied in the screw jack housing. The lifting screws should have grease applied directly to them with a rag or paintbrush. This must be done as part of a regularly scheduled maintenance program.
A driven worm shaft acts on an internal worm gear, which in turn drives a lifting screw to extend or retract. As the lifting screw translates through the jack housing, inherent screw rotation is prevented by an attached load, full guidances or mounting structure that is anchored to resist rotation. The lifting screw will move linearly through the housing to push or pull the load.
What is anti-rotation keyed screw jack?
The lifting screw of a translating screw jack must be attached to the load which prevents the lifting screw from rotating. Otherwise, the lifting screw and the load will turn and not translate. A keyed screw jack can prevent lifting screw rotation, which has milled keyway along the length of the lifting screw. A matching key is fastened to the cover of the jack, which will eliminate jack screw rotation. The keyway in the screw causes greater than normal wear on the internal drive worm gear threads, somewhat reducing screw jack lifespan. Note: jtb series and jtd series ball screw jack anti-rotation devices by square protective pipe with square nut.
What is traveling nut rotating screw jack?
A keyed for traveling nut rotating screw jack features a lifting screw keyed to the internal worm gear as a single unit, forcing the lifting screw to rotate, but not translate. A travelling nut, attached to the load, is driven by the rotation of the lifting screw. This type of jack is ideal for applications that cannot accommodate a screw protective tube or that require a flush mount.
What is the difference between an acme screw jack and a ball screw jack?
The acme screw jack uses an acme threaded screw that is completely self-locking, meaning it will hold its position without a brake mechanism or locking systems. Ball screw jack use ball screws and ball nuts to convert rotary motion to linear movement, and require approx. 1/3 the horsepower compared to a acme screw jack. Due to the efficiency of the ball screw, brake mechanism must be used to stop and hold the lifting screw in position. Brake mechanism is also recommended for use on any screw jack if vibration is present.
Why use an acme screw jack and a ball screw jack?
One type of screw jack is usually better suited to the operating conditions. Typically, fast travel speed and frequent cycle times may be more suited to a ball screw jack, particularly as the load approaches the rated capacity of the screw jack. High load at slow travel speed, less frequent cycles and the ability to hold the load in position when the system is at rest may be better suited for an acme screw jack.
How do I operate the screw jack?
Manual operation, motor driven, or both together.
Various of motors / reducer driven such as 3-phase asynchronous motor, helical gear reducer, worm gear reducer, but air motors and hydraulic motors can also be used. Hand wheel or crank handle can be used for manual operation.
Can I use a larger motor than required in specifications?
Yes, the specifications data is a theoretical value, the motor power should be a little larger than required in specifications, but if the motor power is much more larger than required in specifications, it is not recommended. The screw jack or jack system components could be damaged if an large oversize motor is used. Travel limit switches control must be used for each end of travel to stop the motor. If using solid mechanical stops, screw jack components can be subject to shock load conditions and oversize motors can cause catastrophic failure of stops and other components.
How do I stop the screw jack at the travel limits?
Limit switches or other controls must be used to shut off the motor when the screw jack has reached its full extend or retracted position. Solid mechanical stops are not recommended. Their continued use can cause severe damage to the screw jack.
Can different size screw jacks be used in the same system?
Yes, as long as the equal travel length per full turn of worm shaft input. This is sometimes done to accommodate varying load conditions.
What is the screw jack lifting systems efficiency?
Two screw jack lift system efficiency is 95%.
Three screw jack lift system efficiency is 90%.
Four screw jack lift system efficiency is 85%.
Six screw jack lift system efficiency is 80%.
Miter gearbox efficiency is 95-98%.
Single reduction helical gear reducer efficiency is 98%, Double reduction helical gear reducer efficiency is 97%. Worm gear reducer efficiency is horsepower out x 100 / horsepower in.
What is the maximum input speed?
JACTON screw jack can be run at 1500Rpm. A gear motor, helical gear reducer, or a worm gear reducer is used to reduce the input Rpm to the screw jack to provide the required travel speed of the lifting screw. Many JACTON screw jacks can be driven directly by 1500Rpm and 900Rpm 3-phase motors. Electric motors and gear reducers are available mounted directly to many JACTON screw jacks models.
What causes heat build up in the screw jack?
The screw jack is a mechanical gearbox assembly. The friction of the worm and worm gear set, lifting screw and worm gear set, bearings and seals generate heat while the screw jack is operating. The combination of travel, loading, and input speed all affect the temperature rise of the screw jack. JACTON screw jack sizing calculations take these variables into account to insure that you select the right screw jack model for your application.
What is the screw jack load capacity and travel?
This is based on the relationship of the lifting screw diameter and the length. Lifting screws in tension are rated for the full capacity of the screw jack, regardless of length, providing they do not rotate faster than the critical speed. For the lifting screw in compression, capacity is limited by the screw jack's permissible buckling load. The permissible buckling load of a lifting screw is reduced as the lifting screw gets longer. Use the maximum extended lifting screw length when using the permissible buckling load charts to determine screw jack load capacity.
How do I determine the full-extended lifting screw length?
The extended lifting screw length is normally equal to the travel stroke. If screw jack is equipped with bellows boot and stop nut, must be added the bellows boot full retract length and the addition stop nut or special closed height. These must be increased the extended lifting screw length. For inverted screw jack, the thickness of the mounting structure must be included. This total extended lifting screw length should be used when determining the permissible buckling load of the screw jack.
Should the load being positioned be guided?
It is highly recommended that the load be guided, however, it is not necessary. A guided system will provide more column stability and allow longer screw jack travel. Column length is greatly reduced on unguided systems. External load forces common with unguided systems are detrimental to the life and operation of the screw jack.
Can the screw jack withstand side loading or a bending moment?
Yes, but this is not recommended. Consult JACTON if this condition will be present. These types of loads apply greater forces on the screw jack and housing assembly causing premature wear. Guides are highly recommended and should be used to eliminate side and bending loads.
Can the screw jack withstand shock loading?
This is not recommended. Oversized screw jacks are required to handle shock loads. Solid thrust bearings are also available in many screw jack models when constant vibration and shock are present in an application.
What is the difference between upright and inverted screw jack configurations?
The difference between an upright and an inverted screw jack is the location at which the lifting screw exits the jack relative to the jack gearbox. For example, an upright screw jacks lifting screw exits the jack opposite the gearbox. An inverted screw jacks lifting screw exits the jack on the same side as the gearbox. The choice between inverted and upright screw jack is dependent upon the application.
Note: An upright screw jack mounted upside down is still referred to as an upright screw jack.
How is the linear travel speed calculated?
Each screw jack has an inherent number show lifting screw travel per full turn of worm shaft input. The result of the screw jack is equal to the lifting screw pitch divided by worm gear ratio. For example, JT-10T model screw jack, screw pitch 8mm, high worm gear ratio 1/8, the lifting screw travel is 1mm per full turn of worm shaft input. If 900Rpm is applied to the worm shaft, the linear travel speed is 900Rpm multiplied by 1mm/r, equal to 900 millimeter per minute.
Are screw jacks lubricated prior to shipment?
All JACTON screw jacks are lubricated with a synthetic grease extreme pressure #2 grease before leaving the factory. They are grease lubricated prior to shipment.
What electric motors options are available?
Electric motor options vary among product lines. Customers can use AC 3-phase motor, AC single-phase motor, DC motor. Standard voltage of China is 380V/220V, 3-phase, 50Hz, or 220V, single-phase, 50Hz. Customized international voltage motors like America 110V-single phase-60hz, 240V/480V-three phase-60Hz, other voltages 230V/240V-single phase-50hz, 400V/415V/440V-three phase-50hz etc.
Are screw jacks corrosion resistant?
Stainless steel screw jacks are inherently corrosion resistant. All exposed surfaces are stainless steel and aluminum bronze. Most other screw jacks can be modified with special finishes, coatings, and seals.
Can bellow boots be supplied for an screw jack model with inverted screw?
Yes, but allowance must be made in the length of the lifting screw for both the closed height of the boots and structure thickness. Since we can make no provision for attaching a boot on the underside of your structure, we suggest that a circular plate similar to the lifting screw top plate be welded or bolted to the bottom of your structure supporting the screw jack, thereby making it possible to use a standard bellow boots.
Is there backlash between the lifting screw and worm gear?
Yes. This is necessary to allow for sliding or rolling action of the lifting screw through the worm gear. Anti-backlash nut screw jack is available when the backlash needs to be minimized.
How is the lifting screw protected?
Standard translating screw jack is fitted with a lifting screw protective tube that stores the lifting screw when the screw jack is in the closed position. Bellow boots is available and recommended to protect the lifting screw in the extended position. Double bellows boots are required for rotating screw jack with traveling nut.
How do I attach the load to be positioned to the lifting screw?
For translating screw jack, the lifting screw has a standard threaded end that can be used to attach the load, top plate, clevis end, plain end and forked head are also available. For traveling nut rotating screw design, the traveling nut has a flange with mounting holes. The screw jack gearbox has a mounting base and is also available with a clevis mount for double clevis requirements.
Will the lifting screw rotate?
Yes. You need to prevent the lifting screw from rotating to produce linear motion. The lifting screw will not rotate in a multiple screw jack lift system with all the lifting screws attached to the same structure. If rotation of the screw cannot be prevented in the application design, a anti-rotation keyed screw design jack is available. Input torque will increase for keyed jacks and the capacity may be reduced to 25% of rating.
What is the maximum and minimum operating temperature?
Standard JACTON screw jacks are designed to operate at maximum 80 deg.C (185 deg.F) ambient temperature. For higher temperatures, special grease and seals are required, contact JACTON of these special requirements. Minimum minus 20 deg.C (minus 4 deg.F) ambient temperature. For lower temperatures, special grease and seals are required, contact JACTON of these special requirements.
How do I lubricate a screw screw jack?
Use the proper grease. Fill the housing/gearbox by pumping grease into the grease fittings supplied in the screw jack housing. The lifting screws should have grease applied directly to them with a rag or paintbrush. This must be done as part of a regularly scheduled maintenance program.
Product List
Manual Electric Screw Jack
Worm Screw Jack
- JTC Cubic Screw Jack
- JTM Worm Screw Jack
- JSS Stainless Steel Jack
- JT Acme Screw Jack
- JTW Machine Screw Jack
- Through Holes Screw Jack
- Custom Made Screw Jack
Ball Screw Jack
Bevel Gear Jack
Miter Gearbox
- JT Classic Miter Gearbox
-
- Order Code for Classic Miter Gearbox
- Classic Miter Gearbox description
- JT15 Miter Gearbox
- JT19 Miter Gearbox
- JT25 Miter Gearbox
- JT32 Miter Gearbox
- JT40 Miter Gearbox
- JT45 Miter Gearbox
- JT50 Miter Gearbox
- JT60 Miter Gearbox
- JT72 Miter Gearbox
- JT85 Miter Gearbox
- Flange Input Solid Output Shaft Gearbox
- JTP Cubic Miter Gearbox
-
- Order Code for Cubic Miter Gearbox
- Cubic Miter Gearbox description
- JTP65 Small Miter Gearbox
- JTP90 Miter Gearbox
- JTP110 Miter Gearbox
- JTP140 Miter Gearbox
- JTP170 Miter Gearbox
- JTP210 Miter Gearbox
- JTP240 Miter Gearbox
- JTP280 Miter Gearbox
- Solid Input and Output Shafts Gearbox
- Solid Input and Hollow Output Gearbox
- Flange Input and Solid Output Gearbox
- Flange Input and Hollow Output Gearbox
- JTA Alu. Miter Gearbox
Lift System and Accessories
- Screw Jack System
- Lift System Accessories
-
- Flexible Jaw Coupling
- Overload Safety Couplings
- Aluminum Couplings
- Telescopic Universal Joint
- Rigid Shaft Couplings
- Universal Joint
- Cast Iron Hand Wheel
- Connecting Shafts
- Aluminum Handwheel
- YVF2 Series Variable Speed AC Motor
- Brake motors
- Three Phase Electric Motor
- Screw Jack Motor Flange
- Single Phase Induction Motors
- K Helical Bevel Geared Motor
- R Helical Geared Motor
- Worm Gear Reducer
- 12V 24V DC Geared Motor
- Proximity Switches
- Limit Switches
- Pillow Blocks
- Pillow Block Flange Bearing
- Digital Position Indicator
- Flange Blocks
- Ball Joint Rod End Bearing
- Bellows Boot
- Helical Gear Motor
- 12V 24V DC Motor
- Linear Bushings and Shafts
- Trunnion Adapters
- Servomotor
- Rotary Encoder
- Low Backlash Planetary Gearheads
- Stepper Motor
- 24V Planetary Gear Reducer
- Planetary Speed Reducer
- Frequency Inverter
- Hydraulic Cylinder Rod End Bearing
- Lift System Applications
Linear Actuators
- LAP Electric Linear Actuator
-
- 100KG Parallel Electromechanical Linear Actuators
- 250KG Parallel Electro Mechanical Linear Actuators
- 500KG Parallel Mount Rod Style Linear Actuators
- 630KG Parallel Mount Electric Cylinder Linear Actuators
- 1000KG Parallel Mount Industrial Linear Actuators Acme Screw
- 1600KG Parallel Electro-mechanical Actuators Heavy Duty
- 2500KG Parallel Mount Electric Cylinders Actuator
- 4000KG Heavy Duty Electric Linear Actuators Parallel Mount
- 6300KG Parallel Motor Drive Electric Actuator Linear Actuator
- 8000KG Parallel Electric Motor-Drive Linear Actuator
- 10000KG Parallel Mount Motorized Electric Linear Actuator
- 15000KG Parallel Industrial Motor Linear Actuator
- 20000KG Parallel Indistrial Motor Drive Linear Actuator
- 25000KG Parallel Electric Motor Linear Electric Actuator
- LA Electric Linear Actuators
-
- 10KG In-line Mini Electric Linear Actuators with Brake Motor
- 25KG In-line Electric Linear Actuator Push Rod
- 63KG In-line 700mm Stroke Electric Motor Linear Actuator
- 90KG In-line High Speed Motor Drive Electric Linear Actuator
- 100KG In-line Fast Speed Electric Linear Motor Linear Actuator
- 300KG Inline Industrial Electromechanical Linear Actuator
- 500KG In-Line Electric Linear Actuator
- 700KG Inline Heavy Electro Mechanical Actuators
- 1000KG In-line Heavy Duty AC Volt Industrial Linear Actuators
- JTE Classic Electric Cylinder
- Mechanical Linear Actuators
- JCA Cubic Electric Cylinder
Application
Jacton Industry Co.,Ltd.
Contact: Warren Lee
Skype: jactonjack
T: 86-769-81585810
F: 86-769-81585852
E: sales@jactonindustry.com
W: www.screw-jack.com
Contact: Warren LeeSkype: jactonjackT: 86-769-81585810 F: 86-769-81585852 E: sales@jactonindustry.com W: www.screw-jack.com
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Building 2, No. 1, DongCheng Road, Chang An, Dongguan, Guangdong, China. Phone: 86-769-81585810 | Fax: 86-769-81585852
China Screw Jack,Ball Screw Jack,Machine Screw Jack,Worm Gear Screw Jack,Bevel Gear Screw Jack,Miter Gearbox,Screw Jack Lift System Manufacturer
China Screw Jack,Ball Screw Jack,Machine Screw Jack,Worm Gear Screw Jack,Bevel Gear Screw Jack,Miter Gearbox,Screw Jack Lift System Manufacturer