Mechanical Clamps

Mechanical 1/4 Turn Quick Set Clamps

Mechanical Quick Set Clamps


When to Use 1/4 Turn Quick Set Clamps:

Use mechanical quick set clamps with dies having slotted die plates and enough over slot clearance for the set clamp body.  U-Slot brackets or ears may also be added to the dies or a heel block added to the back of the clamp for some applications.

How they work:

To use, move clamp into position and manually hand tighten nut using the large diameter knurled surface.  Use a wrench to torque to the desired preload.  The large bronze alloy nut acts as an easy turning, anti-galling, large surface thrust bearing arrangement for superior performance.

Model 255 clamps require approximately 125 ft.-lbs. of torque to preload the clamp to 10,000 lbs. clamping force.  Model 259 clamps require approximately 350 ft.-lbs. to preload clamp to 20,000 lbs. clamping force (unlubricated threads).  Clamp preload should be limited to 20,000 lbs. and 40,000 lbs. respectively.

Options and features:

ARA vs. FRA.  Free Rotation (FRA) clamps use standard threaded bolts, while Anti-Rotation (ARA) models use modified threads to prevent the clamping plate from spinning about the bolt.

TSB vs. STN.  Forged T-Slot Bolts (TSB) are standard for production units.  In the case where a larger than standard clamp range is desired, the stud and T-Nut option (STN) is available.

HB Option.  In cases where customers desire to use the clamp in applications without slotted die plates, a heel block may be added to the clamp to support the back of the clamp.  (Clamping force is 50% of rating.)  For this option specify HBX.XX at the end of the part number.  (X.XX = clamping plate height in inches.)

Nut Retention Option.  In cases where customer desires to prevent the nut from coming off the bolt.  A stop mechanism is added to the top of the bolt.  Use TSL in place of TSB in the part number for this option.


Standard Configurations

Model 255 clamps are designed for 3/4” T-Slots and Model 259 for 1” T-Slots. The part number references the “bolt length”, which is not the clamping height, but rather the complete length of the bolt. The charts show nominal clamping height for standard T-Slots. The bolt length can be selected for the part number below.

Model 255
TSB Nominal Clamp Height**
Clamp Range B*
(Standard 3/4” Slot)
Min.     Max.
Min.     Max.
0 – 1 0” 1.125” .75” 2.0” 2.0” 2.5” 4.0”
1 – 2 .875” 2.125” 1.75” 3.0” 2.5” 5.0”
2 – 3 1.875” 3.125” 2.75” 4.0” 2.5” 6.0”
2½ – 4 2.375” 4.125” 3.25” 5.0” 3.0” 7.0”
3 – 5 2.875” 5.125” 3.75” 6.0” 3.5” 8.0”
3½ – 6 3.375” 6.125” 4.25” 7.0” 4.0” 9.0”
Model 259
TSB Nominal Clamp Height**
Clamp Range B*
(Standard 1” Slot)
Min.     Max.
Min.     Max.
0 – ½ 0” .6” .75” 1.6” 2.4” 2.5” 4.0”
¾ – 1½ .75” 1.6” 1.75” 2.6” 2.5” 5.0”
1¾ – 2½ 1.75” 2.6” 2.75” 3.6” 2.5” 6.0”
2¼ – 3½ 2.25” 3.6” 3.25” 4.6” 3.0” 7.0”
2¾ – 4½ 2.75” 4.6” 3.75” 5.6” 3.5” 8.0”
3¼ – 5½ 3.25” 5.6” 4.25” 6.6” 4.0” 9.0”

* T-Slot neck height (dimension A) is assumed to be .875” for 3/4” slots and 1” for 1” slot.

** TSL Style with retaining ring incure a 1/4” reduction in maximum clamp height.

Suffix – STN may replace – TSB if fully threaded stock and T-Nut is cleared for no minimum clamping heights.  Maximum clamping height for STN is calculated as follows:
Model 255 BMAX = E – 3.25
Model 259 BMAX = E – 4.00

Quick Die Change QDC Quick Set turn Clamp Lightning fast Time Saver when installing dies
Quick Die Change QDC Quick Set turn Clamp Lightning fast Time Saver when installing dies - part number specification

Although most PFA products are built to size, the most critical items are maintained on-the-shelf for rapid availability. Need it to ship in 4 hours or less? We can do it! With real-time technical support, off-the-shelf products, and same day shipping, we can often have you back up and running before you've had your morning coffee. That's REAL SERVICE™.


We work with our customers to solve existing problems, and can design custom solutions when needed. With over 25 years of experience reviewing applications and providing custom products, PFA is likely to have the solution to your problem already designed. Call us today and see if we can help!


With a proven off-the-shelf "lean manufacturing" solution from PFA, your application works every time. Using a KOR-LOK® Side-Action System will result in shorter design and manufacturing time and will lead to shorter concept-to-production schedules. KOR-LOK® Preloading Hydraulic Locking Cylinders and Quick Die Change (QDC) clamps are in-stock and ready to ship, so you can start saving time and money with SMED today. From spare parts to complex solutions, PFA is the answer to faster production and more profits.