TJ Davies Retention Knobs Enable High Pull Force

TJ Davies retention knobs are manufactured from American-made 8620 alloy steel that is machined in-house with single point threading to imperial (Class 2A UNC) or metric (Class G6) specifications.

The use of 8620 alloy steel means the components will harden over time, rather than becoming brittle. After threading is completed, each component is heat treated to 58-62 HRC to a depth of 0.020 to 0.030, then treated with hot black oxide to military specifications for protection against corrosion. Each retention knob is magnetic particle tested and then pull tested to 2.5 times the pulling force of the drawbar it is designed for. Full depth is also attained for each thread, and because all machining is done with a single setup, concentricity is achieved.

No carb is applied to the coolant through hole to ensure there is no shrinkage. Core hardness of 40 HRC is standard. All retention knob surfaces have a precision finish of 32 RMA micro or better, ISO grade 6N. Certifications are maintained for each step and each batch to ensure traceability and quality control.

Overtightening can overly stress the retention knob, leading to premature failure, and can cause toolholder swelling and expansion. TJ Davies provides recommended torque guidelines with each retention knob shipped.