Pull Stud (Retention Knob) Torque Specs, Drawbar Force and Replacement

How tight a pull stud should be, how much drawbar force a spindle needs and when to replace a stud, with the values machine builders and tooling makers publish and the source of each. Makers differ, so the table shows them side by side.

Last updated 2 November 2026

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Pull stud tightening torque, as published

The torque that seats a pull stud in the tool holder differs from maker to maker. Use the value of your stud's maker or your machine builder; the table shows what each source publishes (rounded unit conversions in brackets).

Taper (thread)	Haas	BIG DAISHOWA	Lyndex-Nikken	Techniks	Maritool	Hoffmann (SK, maximum)
30 taper (M12, 1/2"-13)	30 ft-lb (40 N·m)	25–30 N·m (18–22 ft-lb)	30–40 ft-lb (41–54 N·m)	36 ft-lb (49 N·m)	20–25 ft-lb (27–34 N·m)	–
40 taper (M16, 5/8"-11)	65 ft-lb (88 N·m)	77–89 N·m (57–66 ft-lb)	65–85 ft-lb (88–115 N·m)	76 ft-lb (103 N·m)	45–55 ft-lb (61–75 N·m)	50 N·m max (37 ft-lb)
45 taper (M20)	–	100–120 N·m (74–89 ft-lb)	–	–	–	–
50 taper (M24, 1"-8)	85 ft-lb (115 N·m)	140–160 N·m (103–118 ft-lb)	85–110 ft-lb (115–149 N·m)	99 ft-lb (134 N·m)	75–90 ft-lb (102–122 N·m)	150 N·m max (111 ft-lb)

How to tighten a pull stud

Tighten with a calibrated torque wrench, holding the tool holder in a fixture. Never hammer the wrench and never use an extension bar: the small end of the taper distorts and the holder chatters (BIG DAISHOWA).
Never tighten a tool or pull stud with the machine spindle (Haas).
Too much torque swells the small end of the taper (bell-mouthing), reduces taper contact and fatigues the stud (T.J. Davies; Cutting Tool Engineering).
Thread-locker advice differs between makers: BIG DAISHOWA applies Loctite to the stud, T.J. Davies uses Loctite 242, Maritool uses medium-strength thread-locker only beyond the first thread of the holder. Follow the stud maker's instruction.

Drawbar clamping force by taper

The drawbar pulls the pull stud, and with it the holder, into the spindle taper. Published values differ in kind: a standard's suggested force, a gripper's maximum or a machine builder's range.

Taper	Value	What it is	Source
CAT30 / CAT40 / CAT45 / CAT50	5,340 / 10,230 / 17,790 / 22,240 N (1,200 / 2,300 / 4,000 / 5,000 lbf)	ASME B5.50 suggested drawbar pull force	TAC Rockford
Steep taper 30 / 40 / 50 / 60	6,000 / 15,000 / 25,000 / 80,000 N (50 reinforced: 35,000 N)	Maximum pull force of the OTT-JAKOB grippers (DIN 69871, ANSI B5.50, MAS 403)	OTT-JAKOB
HSK-A40 / A50 / A63 / A80 / A100	6,800 / 11,000 / 18,000 / 28,000 / 45,000 N	ISO 12164 clamping force	OTT-JAKOB
Haas 40 taper (VF, VM, EC, UMC, GM)	1,460–2,300 lbf (6,494–10,231 N)	Machine builder's range	Haas RD0067
Haas 50 taper (VF, EC)	2,810–4,400 lbf (12,499–19,572 N)	Machine builder's range	Haas RD0067
Haas 30 taper (VF, VM 30K)	600–900 lbf	Machine builder's range	Haas RD0067
Haas HSK-A63	2,835–4,050 lbf (12,610–18,015 N)	Machine builder's range	Haas RD0067

How often to check: OTT-JAKOB recommends testing the pull-in force every six months or every 200,000 tool changes, and acting below 70% of nominal. Haas says a loss of about half the nominal force usually means cracked Belleville spring washers. TAC Rockford treats a change of more than 20–30% from the builder's figure as the warning sign.

PTP's Clamprite gauge measures drawbar force on BT30, BT40, BT50, SK40 and SK50 spindles, with HSK adapters, on 0–14, 0–24 or 0–45 kN dials.

When to replace a pull stud

Haas: about 6,000–8,000 hours of use; replace tool holders and pull studs with surface damage.
BIG DAISHOWA: about a three-year life, shorter with frequent tool changes; inspect at every tool change, because dents from the drawbar balls can lead to breakage.
Maritool: at least every three years, every year for multiple shifts or heavy cuts.
Before each use, look for dimples, grooves or cracks, especially under the head, and check the O-rings of coolant-through studs (T.J. Davies).
Causes of failure named by these sources: fatigue from repeated clamping, corrosion from acidic coolant, low-quality studs, over-tightening and the wrong stud type for the drawbar. A stud that breaks at speed can pull the holder out of the spindle.

Pull stud material and hardness

ISO 7388-3:2007, identical to JIS B 6339-3:2011, specifies a hardness of 55–60 HRC and a tensile strength of at least 980 N/mm² for pull studs, with the thread not hardened.

PTP makes its pull studs of carburizing alloy steel with a tensile strength of 1400–1800 N/mm² and rolled threads; every stud is magnetic-particle tested (MPT) and proof tested at 2.5× the clamping force.

Questions about pull stud torque, force and replacement

What is the torque for a CAT40 or BT40 pull stud?

Published values for 40-taper studs (5/8"-11 or M16) run from 45 to 85 ft-lb (61 to 115 N·m) depending on the maker: Haas specifies 65 ft-lb (88 N·m), BIG DAISHOWA 77–89 N·m, Lyndex-Nikken 65–85 ft-lb, Techniks 76 ft-lb and Maritool 45–55 ft-lb. Hoffmann gives 50 N·m as the maximum for its SK40 stud. Use the value of your stud's maker or your machine builder.

What is the torque for a BT30 pull stud?

Haas specifies 30 ft-lb (40 N·m) for M12 BT30 studs. Other published values: BIG DAISHOWA 25–30 N·m, Lyndex-Nikken 30–40 ft-lb, Techniks 36 ft-lb, Maritool 20–25 ft-lb.

What is the torque for a CAT50 or BT50 pull stud?

Haas specifies 85 ft-lb (115 N·m) for 50-taper studs (1"-8 or M24). Other published values: BIG DAISHOWA 140–160 N·m, Lyndex-Nikken 85–110 ft-lb, Techniks 99 ft-lb, Maritool 75–90 ft-lb; Hoffmann gives 150 N·m as the maximum for its SK50 stud.

What happens if a pull stud is over-tightened?

The stud can swell the small end of the holder's taper (bell-mouthing), which reduces taper contact and causes chatter and vibration, and the stud itself fatigues. BIG DAISHOWA warns never to hammer the wrench or use an extension bar; Haas says never to tighten tools with the spindle. Use a calibrated torque wrench.

What drawbar force does a BT40 or CAT40 spindle need?

No MAS or JIS figure for BT40 was found. ASME B5.50 suggests 10,230 N (2,300 lbf) for CAT40; Haas gives 1,460–2,300 lbf for its 40-taper VF, VM, EC, UMC and GM machines. Measure it with a drawbar force gauge such as the Clamprite and compare with your machine builder's value.

How often should pull studs be replaced?

Haas gives a service life of about 6,000–8,000 hours of use; BIG DAISHOWA about three years, less with frequent tool changes; Maritool at least every three years, or every year with multiple shifts or heavy cuts. Replace any stud with cracks, dents or surface damage at once.

What is the HS code for a pull stud?

US Customs ruling NY N307284 (2019) classified a pull stud bolt under HTS 8466.93.9885 as a machine tool part. Tool holders fall under heading 8466.10 in the US, the EU, the UK and India; India's tariff lists 8466 10 10 for tool holders and 8466 93 10 for parts and accessories of metal-working machine tools. Confirm the code with your customs broker.

How hard should a pull stud be?

ISO 7388-3:2007 (identical to JIS B 6339-3:2011) specifies 55–60 HRC and a tensile strength of at least 980 N/mm², with the thread not hardened. PTP pull studs are made of carburizing alloy steel with a tensile strength of 1400–1800 N/mm², magnetic-particle tested and proof tested at 2.5× the clamping force.