Torque Drivers

  • 0 - 1.5 lb-in and 0 - 75 lb-in Versions Available
  • Accuracy Not Affected by Hand-Hold Position
  • Compatible Hex Drivers and Spanner Bits

TD24 with
1/16" Hex Bit
from the BDSH-KIT






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Item # TD24 TD75
Drive Type Fixed Drive
Square Drive Size 1/4"
Torque Rangea 0 - 1.50 lb-in
(0 - 0.17 N•m)
0 - 75 lb-in
(0 - 8.4 N•m)
Primary Scale
0.3 - 1.5 lb-in
(0.03 - 0.17 N•m)
1.68 - 8.4 N•m
(15 - 75 lb-in)
Primary Scale
1/32 lb-in 0.2 N•m
Secondary Scale
4.8 - 24 oz-in
(0.3 - 1.5 lb-in)
15 - 75 lb-in
(240 - 1200 oz-in)
Secondary Scale
1/2 oz-in 5 lb-in
Dimensions (HxW) 8.1" x 2.3"
(205.7 mm x 58.4 mm)
Weight 1.0 lb (0.45 kg)
  • Although the torque wrenches are operational over the torque range, the 2% accuracy specification is only valid for the primary and secondary capacity spec.
Torque Drivers
Click to Enlarge

Dial faces of the TD24 and TD75 Torque Drivers. The black needle indicates the current torque, while the silver memory needle can be used to indicate the desired torque value.


  • 0 - 1.5 lb-in and 0 - 75 lb-in Versions Available
  • Accurate to 2% of the Reading
  • Metal Precision Dial with Dual Units
  • Memory Needle
  • Not Affected by Hand-Hold Position
  • Compatible Imperial and Metric Hex Drivers and SM-Series Spanner Bits Sold Separately Below

The TD24 and TD75 torque drivers are equipped with a precision metal combination dial, and have a 1/4" square drive socket at the end of the handle. A 1/4"-square-to-1/4"-hex adapter is also included with the TD24 driver for compatibility with the SM-series spanner bits available below. The TD24 can provide 0 to 1.5 lb-in of torque, while the TD75 can provide 0 to 75 lb-in of torque. Both wrenches are accurate to 2% of the dial reading from 20% of the full scale to the full scale. The design of these torque wrenches allows accurate torques to be dialed in regardless of the hand-hold position on the handle.

The precision dial on each driver has two scales. The outer ring of white numbers is the primary scale, and the inner ring of black numbers is the secondary scale. Please see the image to the above right for details. The table to the right lists the increments for each scale. The dial also has two needles. The black needle indicates the torque that is being applied to a fixture. The silver memory needle is moveable and can be used to more clearly indicate the desired torque value.

An accurate set of torque wrenches is essential for assembling high-performance optomechanical systems, and when using ultra-stable mounts, such as our Polaris® kinematic mirror mounts. Tightening screws to a proper torque and maintaining consistency and repeatability is important because stresses from over torquing can easily distort an optic, warp a flat optical mounting surface, or add excessive stress that will relieve over time and cause mechanical creep.

The TD24 has a range that is optimal for setting an optic without applying excessive force. The setscrew that holds an optic into the mount should only be torqued to approximately 0.38 to 0.75 lb-in in most applications. Less torque will result in an optic being too loose and excessive torque will result in an optic being distorted or damaged.

The TD75 has a range that is optimal for building optomechanical systems. Applying proper torque to components will ensure that your system is built to a repeatable standard and remove the risk of components being loose or over-tightened.

The wrenches are shipped with the main pointer on the dial lined up with the zero mark and pointing away from the handle. If the main pointer ever does not return to the zero mark, hold the outer dial ring and turn it until they line up again. This will not affect the calibration of the tools. These drivers are shipped with a certification of calibration.

To achieve accurate torque readings the following method may be used:

Rotate the knurled knob counterclockwise (clockwise if you are using the driver in the counterclockwise direction) on top of the crystal until the silver memory needle contacts the main black pointer. Turn the dial bezel counterclockwise until the silver memory needle is pointing to zero. Place the torque driver on the fastener, making sure the tool remains parallel with the fastener. Twist the handle until the desired torque is achieved. When the pressure is released, the black pointer will return to zero, but the silver memory needle will remain at the peak torque reached.

Be sure that the torque wrench is properly zeroed before each use. After each use, make sure the black pointer returns to zero, or the pre-set value. For the most accurate reading, the final turn of the fastener should be made with the torque wrench.

Never use the torque wrench to loosen a tightened screw as it may exceed the maximum torque value of the driver. Never push the needle past the maximum range of the torque driver.

Posted Comments:
Alessandro Manelli  (posted 2021-11-26 12:06:11.07)
Dear Thorlabs, Where is possible to find the tightening torque to apply to your optical elements? is it dependent by the optical element itself or optical element and type of mounting used?
cdolbashian  (posted 2021-12-23 02:05:45.0)
Thank you for reaching out to us Alessandro! As your second question indicates, it is indeed dependent both on the mount, and on the optic being mounted. I would add that it also depends on your application. We have some guidelines for torque spec on our POLARIS line of high precision mounts, but for our standard mounts, we have no such specs. Please feel free to view the front mounted POLARIS torque specs here:
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Torque Drivers

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
TD24 Support Documentation
TD24Customer Inspired! Torque Driver, 0 - 1.5 lb-in
TD75 Support Documentation
TD75Customer Inspired! Torque Driver, 0 - 75 lb-in
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Hex Driver Bits

These Hex Driver Bit Kits are compatible with our TD24 and TD75 torque drivers (sold above) as well as traditional 1/4" socket wrenches. The hex sizes available correspond with many of the hex screws used in our broad product line. Each bit is engraved with the hex size as seen in the photo to the right.

Please refer to the engraving on the bit for the appropriate hex size. The sockets have engraved sizes on them that may not match the engraved sizes on the hex bit.

Hex Driver Bit Kit Contents
Imperial Kit 0.050", 1/16", 5/64", 3/32", 7/64", 1/8", 9/64", 5/32", and 3/16"
Metric Kit 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, 4.0 mm, and 5.0 mm
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Imperial Price Available
BDSH-KIT Support Documentation
BDSH-KITCustomer Inspired! 9-Piece, 1/4" Bit Driver Square Drive to Hex Kit, Imperial
+1 Qty Docs Part Number - Metric Price Available
BDSH-KIT/M Support Documentation
BDSH-KIT/MCustomer Inspired! 6-Piece, 1/4" Bit Driver Square Drive to Hex Kit, Metric
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Spanner Bits for SM-Series Retaining Rings

Spanner Bit and Torque Driver Application
Click to Enlarge

Spanner Bits and the TD24 Torque Driver Can Be Used to Mount Optics in SM-Threaded Polaris® Mirror Mounts
  • Bits Available for SM05, SM1, SM1.5SM2, and SM3 Retaining Rings
  • 1/4" Hex Shank Fits Adapter Included with TD24 Torque Driver
  • Ideal for Installing or Adjusting SM-Series Retaining Rings without Damage When Paired with the TD24 Torque Driver

These spanner bits can be used with our TD24 Torque Driver to install or adjust SM-series retaining rings without damaging optics that may be in place. A square-to-hex adapter is included with the TD24 Torque Driver that allows the bits to be attached. Please note that the torque range and resolution of the TD75 Torque Driver makes it unsuitable for tightening optics.

Various spanner bits are available for compatibility with SM05 (0.535"-40), SM1 (1.035"-40), SM1.5 (1.535"-40), SM2 (2.035"-40), and SM3 (3.035"-40) retaining rings. Each bit includes guide flanges that prevent most optical elements from being scratched while the bit is being inserted. When using lenses with high curvature, we recommend the SPW801 Adjustable Spanner Wrench, which uses long blades that prevent scratches caused by the guide flanges.

A spanner wrench bit kit is also available which includes bits for SM05, SM1, and SM2 retaining rings, a driver handle with a 1/4" hex socket, and case.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
SPB05 Support Documentation
SPB05SM05 Spanner Bit
SPB1 Support Documentation
SPB1SM1 Spanner Bit
SPB1.5 Support Documentation
SPB1.5Customer Inspired! SM1.5 Spanner Bit
SPB2 Support Documentation
SPB2SM2 Spanner Bit
SPB3 Support Documentation
SPB3SM3 Spanner Bit