
- Lifting Equipment
-
Height Safety
Height Safety Equipment
- Material Handling & Jacking Equipment
- Shop by Brand
- Clearance
-
Contact
Get In Touch
- Home/
- Lifting Equipment/
- Screwjacks, Linear Actuators, Rotary Unions and ACME Ball Screws and Nuts/
- Duff Norton Screwjacks/
- Stainless Steel Anti-Backlash Machine Screwjack Actuator, 2t to 150t
Stainless Steel Machine Screw Actuator
Stainless Steel Anti-backlash actuators reduce vertical backlash resulting in smooth, precise operation and minimal wear along with the same great corrosion resistance offered by our standard stainless steel actuators.
Backlash occurs when the motor driving an actuator reverses its load direction.
Since there is a gap between the lifting screw and the worm gear threads detrimental screw movement may occur.
When the actuator is under load, the lifting screws threads are supported by the worm gears threads.
The anti-backlash nut, being pinned by to the worm gear and being adjusted downwards by the shell cap, forces the bottom thread surfaces against the upper thread surfaces of the lifting screw, Thus backlash between the lifting screw and worm gear threads is reduced to a minimum.
- The Duff Norton Anti-backlash design features a separate anti-backlash nut and reduces actuator backlash to less than 1 thousandths.
- Available with either 316SS or 17-4PH worm.
- Anti-backlash nuts reduce worm gear wear.
- Anti-backlash nuts act as additional load safety devices when the worm gear has become worn.
Key Adaptor Dimensions for Anti-Backlash Actuators

Actuator Capacity (tons) | Upright A Dia. (in) | Upright B (in) | Upright C (in) | Inverted D Dia. (in) | Inverted E (in) | Inverted F (in) |
1/4 & 1/2 | 1.66 | Pipe Length | 2.38 | 1.25 | .81 | 2.88 |
1 | 1.66 | .75 | 3.84 | 1.50 | .38 | 3.38 |
2 | 2.25 | 1.25 | 3.88 | 2.25 | .63 | 3.88 |
3 | 2.25 | 1.25 | 4.34 | 2.25 | .63 | 4.34 |
5 | 2.75 | 1.75 | 5.44 | 2.75 | .88 | 5.44 |
10 | 3.38 | 2.00 | 5.75 | 3.38 | 1.13 | 5.75 |
15 | 3.63 | 2.00 | 6.13 | 3.63 | 1.25 | 6.13 |
20 | 4.00 | 1.50 | 7.75 | 4.00 | 1.00 | 7.75 |
25 | 5.50 | 2.25 | 9.69 | 5.50 | 1.25 | 9.69 |
35 | 6.50 | 2.38 | 9.44 | 6.50 | 1.25 | 9.44 |
50 | 7.00 | 3.00 | 11.75 | 7.00 | 3.00 | 11.75 |
Stainless Steel Anti-Backlash Actuators Performance Specifications
Capacity (tons) - 17-4PH Worm | 2 | 5 | 10 | 15 | 20 | 25 | 35 | 50 | 100 | |
Capacity (tons) - 316 SS Worm | 0.67 | 1.66 | 3.33 | 5.00 | 6.66 | 8.33 | 11.66 | 16.66 | 33.33 | |
Lifting Screw | Diameter (in) | 1 |
1 1/2 |
2 |
2 1/4 |
2 1/2 |
3 |
3 3/4 |
4 1/2 |
6 |
Pitch (in) | 0.250 |
0.375 |
0.500 |
0.500 |
0.500 |
0.666 |
0.666 |
0.666 |
0.750 |
|
Type | ACME | ACME |
ACME |
ACME |
ACME |
ACME |
ACME |
Mod.Sq. |
Mod.Sq. |
|
Worm Gear Ratios | Standard | 6:1 | 6:1 |
8:1 |
8:1 |
8:1 |
10 2/3:1 |
10 2/3:1 | 10 2/3:1 | 12:1 |
Optional Number 1 | 24:1 |
24:1 |
24:1 |
24:1 |
24:1 |
32:1 |
32:1 |
32:1 |
36:1 |
|
Optional Number 2 | 12:1 | 12:1 |
- |
- |
- |
- |
- |
- |
- |
|
Turns of Worm for 1" Raise | Standard | 24 | 16 |
16 | 16 |
16 | 16 |
16 | 16 | 16 |
Optional Number 1 | 96 | 64 | 48 |
48 |
48 |
48 |
48 |
48 |
48 |
|
Optional Number 2 | 48 | 32 |
- |
- |
- |
- |
- |
- |
- |
|
Worm Torque at No Load (in-lb) | Standard | 5 |
10 |
20 |
20 |
30 |
40 |
50 |
100 |
200 |
Optional Number 1 | 5 | 10 |
20 |
20 |
30 |
40 |
50 |
100 |
200 |
|
Optional Number 2 | 5 | 10 |
- |
- |
- |
- |
- |
- |
- |
|
Maximum Horsepower per Actuator | Standard | 2 | 4 |
5 |
5 |
5 |
8 |
8 |
15 |
25 |
Optional Number 1 | 1/2 | 3/4 |
1 1/2 |
1 1/2 |
1 1/2 |
2 1/2 |
2 1/2 |
6 |
11 |
|
Optional Number 2 | 3/4 | 2 |
- |
- |
- |
- |
- |
- |
- |
|
Worm Torque at Full Load (in-lb) 17-4PH Worm | Standard | 120 | 450 |
750 |
1430 |
2050 |
2700 |
4000 |
7500 |
16000 |
Optional Number 1 | 50 | 185 |
400 |
820 |
1170 |
1700 |
2400 |
4200 |
8600 |
|
Optional Number 2 | 75 | 275 |
- |
- |
- |
- |
- |
- |
- |
|
Worm Torque at Full Load (in-lb) 316SS Worm | Standard | 43 | 156 | 263 | 490 | 703 | 926 |
1366 |
2566 |
5466 |
Optional Number 1 | 20 | 68 |
147 |
287 |
410 |
593 |
833 |
1466 |
3000 |
|
Optional Number 2 | 28 |
98 |
- |
- |
- |
- |
- |
- |
- | |
Efficiency Rating (%) | Standard | 20.4 | 21.2 | 25.2 | 20.3 | 18.9 | 17.9 |
17.0 |
12.9 |
12.1 |
Optional Number 1 | 11.1 |
12.1 |
15.1 |
11.6 |
10.8 |
9.3 | 9.3 |
7.5 |
7.4 |
|
Optional Number 2 | 15.6 | 16.8 | - |
- |
- |
- |
- |
- |
- |
|
Weight with 6" Raise (lb) | 17 | 35 | 52 | 66 | 93 | 160 | 240 |
410 |
1200 |
|
Weight per Additional 1" Raise (lb) | 0.3 | 0.9 | 1.4 | 1.5 | 2.6 | 2.5 |
3.7 |
5.5 |
9.0 |
|
Key Torque (in-lb) | 153 |
581 |
1565 |
2527 |
3538 |
4665 |
8828 |
15697 |
39396 |
|
Max Worm Speed at Full Load (rpm) | Standard | 1750 | 1615 |
1198 |
643 |
449 |
544 |
369 |
368 |
288 |
Optional Number 1 | 1576 | 694 | 645 |
330 |
231 |
266 |
189 |
258 |
231 |
|
Optional Number 2 | 1669 | 1286 |
- |
- |
- |
- |
- |
- |
- |
|
Max Load at Full Horsepower and 1750 rpm (lb) | Standard | 1333 | 3047 |
4386 |
3406 |
2972 |
4664 |
4220 |
5949 |
8865 |
Optional Number 1 | 1156 | 972 |
1791 |
1276 |
843 |
1507 |
1192 |
2831 |
4671 |
|
Optional Number 2 | 1258 | 2339 | - |
- | - | - | - | - | - |

How it Works
When the screw (1) is under a compression load, the bottom of its thread surfaces are supported by the top thread surfaces of the worm gear (2). The anti-backlash nut (3), being pinned to the worm gear and floating on these pins and being adjusted downwards by the shell cap, forcing its bottom thread surfaces against the upper thread surfaces of the lifting screw at point (B).
Thus backlash between the worm gear threadsand the lifting screw threads is reduced to a regulated minimum.
When wear occurs in the worm gear threads and the anti-backlash nut thread, the load carrting thickness of the worm gear thread will be reduced. This wear will create a gap at point (B) and provide backlash equal to the wear on the threads.
Under a compression load, the lifting screw will no longer be in contact with the lower thread surface of the anti-backlash nut. Under this condition, backlash will be present when a tension load is applied. The anti backlash feature can be maintained simply by adjusting the shell cap until the desired amount of backlash reduction is achieved.
This will reduce the separation (A) between the anti- backlash nut and the worm gear and will reduce the backlash between the worm gear threads and the lifting screw to the desired minimum value.
To avoid binding and excessive wear, do not adjust lifting screw backlash to less than .0005".
When separation (A) has been reduced to zero, the wear limit has been reached.
Replace the worn gear and backlash nut set at this point.
This feature acts as a built in safety device.
Stainless Steel Machine Screw Actuator
Stainless Steel Anti-backlash actuators reduce vertical backlash resulting in smooth, precise operation and minimal wear along with the same great corrosion resistance offered by our standard stainless steel actuators.
Backlash occurs when the motor driving an actuator reverses its load direction.
Since there is a gap between the lifting screw and the worm gear threads detrimental screw movement may occur.
When the actuator is under load, the lifting screws threads are supported by the worm gears threads.
The anti-backlash nut, being pinned by to the worm gear and being adjusted downwards by the shell cap, forces the bottom thread surfaces against the upper thread surfaces of the lifting screw, Thus backlash between the lifting screw and worm gear threads is reduced to a minimum.
- The Duff Norton Anti-backlash design features a separate anti-backlash nut and reduces actuator backlash to less than 1 thousandths.
- Available with either 316SS or 17-4PH worm.
- Anti-backlash nuts reduce worm gear wear.
- Anti-backlash nuts act as additional load safety devices when the worm gear has become worn.
Key Adaptor Dimensions for Anti-Backlash Actuators

Actuator Capacity (tons) | Upright A Dia. (in) | Upright B (in) | Upright C (in) | Inverted D Dia. (in) | Inverted E (in) | Inverted F (in) |
1/4 & 1/2 | 1.66 | Pipe Length | 2.38 | 1.25 | .81 | 2.88 |
1 | 1.66 | .75 | 3.84 | 1.50 | .38 | 3.38 |
2 | 2.25 | 1.25 | 3.88 | 2.25 | .63 | 3.88 |
3 | 2.25 | 1.25 | 4.34 | 2.25 | .63 | 4.34 |
5 | 2.75 | 1.75 | 5.44 | 2.75 | .88 | 5.44 |
10 | 3.38 | 2.00 | 5.75 | 3.38 | 1.13 | 5.75 |
15 | 3.63 | 2.00 | 6.13 | 3.63 | 1.25 | 6.13 |
20 | 4.00 | 1.50 | 7.75 | 4.00 | 1.00 | 7.75 |
25 | 5.50 | 2.25 | 9.69 | 5.50 | 1.25 | 9.69 |
35 | 6.50 | 2.38 | 9.44 | 6.50 | 1.25 | 9.44 |
50 | 7.00 | 3.00 | 11.75 | 7.00 | 3.00 | 11.75 |
Stainless Steel Anti-Backlash Actuators Performance Specifications
Capacity (tons) - 17-4PH Worm | 2 | 5 | 10 | 15 | 20 | 25 | 35 | 50 | 100 | |
Capacity (tons) - 316 SS Worm | 0.67 | 1.66 | 3.33 | 5.00 | 6.66 | 8.33 | 11.66 | 16.66 | 33.33 | |
Lifting Screw | Diameter (in) | 1 |
1 1/2 |
2 |
2 1/4 |
2 1/2 |
3 |
3 3/4 |
4 1/2 |
6 |
Pitch (in) | 0.250 |
0.375 |
0.500 |
0.500 |
0.500 |
0.666 |
0.666 |
0.666 |
0.750 |
|
Type | ACME | ACME |
ACME |
ACME |
ACME |
ACME |
ACME |
Mod.Sq. |
Mod.Sq. |
|
Worm Gear Ratios | Standard | 6:1 | 6:1 |
8:1 |
8:1 |
8:1 |
10 2/3:1 |
10 2/3:1 | 10 2/3:1 | 12:1 |
Optional Number 1 | 24:1 |
24:1 |
24:1 |
24:1 |
24:1 |
32:1 |
32:1 |
32:1 |
36:1 |
|
Optional Number 2 | 12:1 | 12:1 |
- |
- |
- |
- |
- |
- |
- |
|
Turns of Worm for 1" Raise | Standard | 24 | 16 |
16 | 16 |
16 | 16 |
16 | 16 | 16 |
Optional Number 1 | 96 | 64 | 48 |
48 |
48 |
48 |
48 |
48 |
48 |
|
Optional Number 2 | 48 | 32 |
- |
- |
- |
- |
- |
- |
- |
|
Worm Torque at No Load (in-lb) | Standard | 5 |
10 |
20 |
20 |
30 |
40 |
50 |
100 |
200 |
Optional Number 1 | 5 | 10 |
20 |
20 |
30 |
40 |
50 |
100 |
200 |
|
Optional Number 2 | 5 | 10 |
- |
- |
- |
- |
- |
- |
- |
|
Maximum Horsepower per Actuator | Standard | 2 | 4 |
5 |
5 |
5 |
8 |
8 |
15 |
25 |
Optional Number 1 | 1/2 | 3/4 |
1 1/2 |
1 1/2 |
1 1/2 |
2 1/2 |
2 1/2 |
6 |
11 |
|
Optional Number 2 | 3/4 | 2 |
- |
- |
- |
- |
- |
- |
- |
|
Worm Torque at Full Load (in-lb) 17-4PH Worm | Standard | 120 | 450 |
750 |
1430 |
2050 |
2700 |
4000 |
7500 |
16000 |
Optional Number 1 | 50 | 185 |
400 |
820 |
1170 |
1700 |
2400 |
4200 |
8600 |
|
Optional Number 2 | 75 | 275 |
- |
- |
- |
- |
- |
- |
- |
|
Worm Torque at Full Load (in-lb) 316SS Worm | Standard | 43 | 156 | 263 | 490 | 703 | 926 |
1366 |
2566 |
5466 |
Optional Number 1 | 20 | 68 |
147 |
287 |
410 |
593 |
833 |
1466 |
3000 |
|
Optional Number 2 | 28 |
98 |
- |
- |
- |
- |
- |
- |
- | |
Efficiency Rating (%) | Standard | 20.4 | 21.2 | 25.2 | 20.3 | 18.9 | 17.9 |
17.0 |
12.9 |
12.1 |
Optional Number 1 | 11.1 |
12.1 |
15.1 |
11.6 |
10.8 |
9.3 | 9.3 |
7.5 |
7.4 |
|
Optional Number 2 | 15.6 | 16.8 | - |
- |
- |
- |
- |
- |
- |
|
Weight with 6" Raise (lb) | 17 | 35 | 52 | 66 | 93 | 160 | 240 |
410 |
1200 |
|
Weight per Additional 1" Raise (lb) | 0.3 | 0.9 | 1.4 | 1.5 | 2.6 | 2.5 |
3.7 |
5.5 |
9.0 |
|
Key Torque (in-lb) | 153 |
581 |
1565 |
2527 |
3538 |
4665 |
8828 |
15697 |
39396 |
|
Max Worm Speed at Full Load (rpm) | Standard | 1750 | 1615 |
1198 |
643 |
449 |
544 |
369 |
368 |
288 |
Optional Number 1 | 1576 | 694 | 645 |
330 |
231 |
266 |
189 |
258 |
231 |
|
Optional Number 2 | 1669 | 1286 |
- |
- |
- |
- |
- |
- |
- |
|
Max Load at Full Horsepower and 1750 rpm (lb) | Standard | 1333 | 3047 |
4386 |
3406 |
2972 |
4664 |
4220 |
5949 |
8865 |
Optional Number 1 | 1156 | 972 |
1791 |
1276 |
843 |
1507 |
1192 |
2831 |
4671 |
|
Optional Number 2 | 1258 | 2339 | - |
- | - | - | - | - | - |

How it Works
When the screw (1) is under a compression load, the bottom of its thread surfaces are supported by the top thread surfaces of the worm gear (2). The anti-backlash nut (3), being pinned to the worm gear and floating on these pins and being adjusted downwards by the shell cap, forcing its bottom thread surfaces against the upper thread surfaces of the lifting screw at point (B).
Thus backlash between the worm gear threadsand the lifting screw threads is reduced to a regulated minimum.
When wear occurs in the worm gear threads and the anti-backlash nut thread, the load carrting thickness of the worm gear thread will be reduced. This wear will create a gap at point (B) and provide backlash equal to the wear on the threads.
Under a compression load, the lifting screw will no longer be in contact with the lower thread surface of the anti-backlash nut. Under this condition, backlash will be present when a tension load is applied. The anti backlash feature can be maintained simply by adjusting the shell cap until the desired amount of backlash reduction is achieved.
This will reduce the separation (A) between the anti- backlash nut and the worm gear and will reduce the backlash between the worm gear threads and the lifting screw to the desired minimum value.
To avoid binding and excessive wear, do not adjust lifting screw backlash to less than .0005".
When separation (A) has been reduced to zero, the wear limit has been reached.
Replace the worn gear and backlash nut set at this point.
This feature acts as a built in safety device.
You May Also Like
Contact Us About This Product
If you wish to receive a quote for this product, please use the tab above, this form is for general enquiries regarding this product only.
You can also Request a Quote using the Quote tab above!
You can easily add more than one item to the Quote Request. This is highly recommended as we will be able to suit your needs much more efficiently.