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About Retention Knobs / Pull Studs

We offer arguably the largest variety of retention knobs in the United States. We offer USST, Lyndex and Parlec knobs in CAT and BT Tapers. If you cannot find the correct retention knob, please call and let us help you locate the correct knob for your machine.

Why Choose USST™ Retention Knobs?

  • Each retention knob is certified free of cracks after being INDIVIDUALLY Magnetic Particle Tested by an Independent Nationally Certified Laboratory in the U.S. to ensure knob integrity (ASTM E1444-01)
  • Manufacturing date, batch number and part number are all clearly laser marked on each retention knob
  • Knobs are made to applicable standards (ANSI, JMTBA, DIN)
  • Pilots now standard on a majority of CAT & BT Taper knobs for better seating and improved concentricity
  • Coolant holes are left non-carburized
  • Made from 8620, heat-treated to RC 56/58
  • Stronger threads resulting from thread rolling on a vast majority of the knobs
  • High quality black oxide treatment to ensure long life
  • Made in USA


Machine tool manufacturers use various styles and sizes of retention knobs. They often look similar and appear to be interchangeable, but in reality they are not. It is very important not to interchange metric retention knobs with inch toolholders. The use of the incorrect knob, or the incorrect usage of a knob, may result in injury or property damage. To ensure choosing the correct knob, please use the following guidelines:

  1. Specify the make model and spindle size of your machine.
  2. Make sure that the “critical dimensions” are correct. The retention knob print, usually found in the machine manual, is one of the best tools for selection of the correct knob.
  3. The part number of previously used retention knobs from any manufacturer can also help us provide you with the correct knob for your machine. Our database contains most manufacturer’s part numbers.

We try to insure that we specify the correct knob, however, it is the responsibility of the end user to check that the supplied knobs are correct for the machine tool and taper type.


Machining Center manufacturers have increased the draw bar force on retention knobs frequently in recent years. It is now more important than ever to check your retention knobs periodically. Remember to fully tighten the retention knob. Failure to do so may result in the toolholder coming loose during operation.


A machine out of alignment or used beyond capacity can cause failure. Metal fatigue, over time, can also cause failure. Retention knobs should be inspected periodically and replaced. Any signs of wear or damage indicate that the retention knobs should be replaced. Every 2 to 3 years, depending on use, knobs should be removed from the holder and inspected. Any retention knobs showing indications of cracking must be discarded. If your machine has been in a collision, or releases a tool prematurely, this is may be an indication that the retention knob fingers, finger guide, belleville washers or the retention knob itself may be damaged. The machine tool should not be used until inspected by Maintenance or Factory trained personnel. In this case, all of the machine’s retention knobs should be checked for cracks or damage immediately.

Over-tightening of the retention knob may result in bulging of the toolholder. Retention knob sockets and torque wrenches are highly recommended to ensure the correct tightness.

A worn knob is extremely detrimental to the TIR of a toolholder and replacing your retention knob is an easy and inexpensive way to improve the accuracy of the toolholder by up to 10X!
Best Practices for Retention Knob Usage:
  • Store unused knobs carefully so the knobs do not get dented, scratched or nicked in storage.
  • Use the correct knob for the tool machine and the tool holder.
  • Log the installation date.
  • Properly tighten the knobs at all times per the machine manufacturer recommendations. Use a torque wrench. Over-tightening or under-tightening are both detrimental.
  • Do not use glue or binding compound on the knobs.
  • Inspect and clean knobs regularly.
  • Unusual wear on the knobs may indicate other problems with gripper or the feed fingers. You should only see a uniform set of slight indentations from your grip fingers.
  • Change O-ring on a regular basis.
  • Replace the retention knobs regularly every two years, depending on the operation.
  • Replace knobs more often for tools used in roughing.