Screw Jack: Definition, Working, Types, Applications(with Pdf)

Today, I am going to discuss Screw Jack.

If you are looking to know about the same, then I invite you to come with me and join the journey with Engineers Rail.

Before I start, here is the gift for you, you can take out this whole article as a pdf at the end of the article.

So, let’s begin with the basics…

What is Jack screw?

Basically, a Screw jack is used to lift the weight using rotational motion into push-pull linear motion using screw square thread.

The rotational motion can be provided manually or electrically using motors.


The main working principle behind the jackscrew is the inclined plane. The Screw thread situated on the nut is the heart of the screw jacks.

When the load is placed on the head, it can be lifted up and down by rotating the lever arm or handle in the clockwise direction and vice-versa. This rotation causes to climb up and down the linear pitches or threads and thus load moves up and down with less effort applied.

Screw jack diagram-

screw jack diagram


There are simply two types of screw jack-

  1. Simple Screw jack
  2. Differential Screw jack

Simple Screw jack-

A simple screw jack is a simple lifting machine, where a simple mechanism of lifting is used to lift the heavy loads applying marginally less effort. The simple screw jack is also known as a Manual screw jack.

Simple screw jacks consists of

  • Base
  • Bolt
  • Threaded area
  • Head

Firstly, the cone-shaped base area is given to support the lifting mechanism, and above the base, the bolt is given to regulate the square shape thread and prevent it from slipping, when the load is applied.

The threaded area is consists of the lead screw with square thread. The lead screw counts as the best screw to lift heavyweight. This lead screw is used in various heavyweight machines like lathe machines, drill machines etc.

Lastly, the head where the existing load is applied to lift by applying less effort. The application of the simple screw jack is in car lifting, heavy-vehicle lifting to repair or change the damaged equipment and so on.

simple screw jack diagram

Here is some simple jackscrew formula-

The velocity ratio of simple screw jack,

V.R.= πD/p

 Where D= diameter of the head and p= pitch gap

The Mechanical advantage of simple screw jack,

M.A.=  W/P

where W= applied load and P= applied effort.

And, the efficiency of simple jackscrew,

η= (M.A/V.R)×100

Differential Screw Jack-

A differential screw jack is an upgraded version of a simple screw jack where a differential screw is used to increase the velocity ratio of the differential screw jack.

The same effort is required to lift larger loads than a simple screw jack. It is also known as a compound screw jack or Hunter screw jack.

Differential screw jack provides increased velocity ratio as compared to simple screw jack.

Now, you may be wondering, why it is called differential jackscrew?

So, the difference between the thread sizes and their pitches is the cause behind the name of differential jack.

Now, Let’s see the diagram of the differential screw jacks.

diagram of differential screw jack

This mechanism consists of two different screw threads A and B, shown in the figure. The A portion is threaded internally and externally. The outer thread of portion A will rotate with the base nut with a fixed lever arm on the top of the A portion, as you can see in the figure.

The internal threading will give space to rotate Portion B inside. When the lever arm moves clockwise, portion A will go down toward the base nut and this cause to uplift portion B and vice-versa, and hence lifting the load with less amount of effort than a simple jackscrew.

Therefore, the total distance travelled by both of the threads-  PA-PB


The velocity ratio of differential screw jack

V.R= 2πR/PA-PB


And, The mechanical advantage of differential screw jack-

                                                          M.A= 2πR/PA-PB                                                                (∴η=1)


Now, Lets look at the various applications of screw jacks-


Here are some applications of the same-

To lift heavy loads- a jackscrew is used to lift heavy loads such as car, trucks to repair or change the damaged parts inside. It is also used in aircraft.

To adjust foundations- Some of the screw jacks are used to uplift the houses from its foundations.

To uplift and lift down the loads- This is mainly used to uplift or down lift the heavy machinery in various industries.

Wrapping up-

Screw jacks are very fundamentals and important equipment in the mechanical industries which you have learned above in a very fundamental way, from scratch to end.

I hope you like spending time here and in return, you gained some knowledge. If so, share with your friends or colleagues or needy ones. Sharing links are done below, Hit any of your preferred ones.

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Here are some suggested article, you should consider-

Riveted Joints: Definition, Types, Uses, Efficiency, Advantages and More

11 Types of rivets & Basic uses with Diagram

Thank you for being with me. I hope to see you in the next sesssion.


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screw jack pdf screw jack pdf


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