NT30 collet chucks and tool holders (DIN 2080)

NT is the manual tool-change branch of the 7:24 family. It shares the taper and the gauge diameter with BT30, ISO30 and CAT30 — and that is exactly why it is so easy to buy the wrong holder. The difference is at the back of the holder, not the front.

What NT actually means

NT is the traditional pattern specified by DIN 2080, and in Chinese catalogues it is frequently called ST. The five widely quoted standards for 7:24 holders are NT (DIN 2080), DIN 69871, ISO 7388/1, MAS BT and ANSI/ASME — and of those five, NT is the only one held by a drawbar rather than by a pull stud. That single fact explains every other difference on this page.

There is no pull stud on an NT holder. The drawbar runs the length of the spindle and threads directly into the back of the holder. Because nothing grabs the holder from outside, NT is a manual tool change system — which is why it is found on conventional milling machines, toolroom mills and older Japanese equipment rather than on machining centres with an automatic changer.

Drawbar threads — three families, one size

NT tooling is listed with a metric, a Whitworth or a UNC drawbar thread depending on the maker and the age of the machine. All three are in circulation for the same nominal size.
Size	Metric	Whitworth	UNC	Gauge Ø (mm)
NT30	`M12`	W 1/2	1/2"-12	31.75
NT40	`M16`	W 5/8	5/8"-11	44.45
NT50	`M24`	W 1	1"-8	69.85
NT60	`M30`	W 1¼	1¼"-7	107.95

Confidence levels differ by column — we have kept them separate.

The metric and Whitworth columns are well corroborated across holder references.
The UNC column comes from a single holder maker's draw-bolt specification, and that same source gives the pitches as M12×1.75, M16×2.0, M24×3.0 and M30×3.5. We found no second source for either the UNC sizes or the pitches, so thread-check your own drawbar before ordering.
If an NT holder will not thread onto your drawbar, suspect a Whitworth or UNC part before concluding anything is broken. This is the most common NT ordering mistake.

NT30 vs BT30 vs ISO30 vs CAT30

All four are 7:24, and all four have a gauge diameter of 31.75 mm on a size 30. A holder from one will physically seat in another's spindle. That is the problem.

	NT30 (DIN 2080)	BT30 (MAS 403)	CAT30 (ASME B5.50)
Tool change	Manual	Automatic	Automatic
Retained by	Drawbar into holder tail	Pull stud gripped by the changer	Pull stud gripped by the changer
Pull stud	None	Yes — M12	Yes — M12
Tail thread	Drawbar thread M12	Stud thread M12	Stud thread M12
Drive	Keyway in the bore	Drive keys on the flange	Drive keys on the flange
Flange form	Asymmetric, no ATC gripper groove	Symmetric with gripper groove	V-flange with gripper groove

Both NT30 and BT30 show an M12 thread at the tail — do not read that as compatibility. In one case the drawbar threads into it from inside the spindle; in the other a pull stud screws into it so a gripper has something to grab. A BT holder in an NT spindle has no pull stud for anything to grip and no drive-key engagement to stop it rotating, and an NT holder in a BT spindle has nothing for the changer to hold. Same taper, same gauge diameter, same thread size, wrong part.

Which collet chuck to buy for an NT30 spindle

An NT30 spindle takes NT30-shank chucks. In practice almost everyone buys one of two things:

Option	Covers	Choose it when
NT30-ER32 collet chuck	ER32 collets, 3 – 20 mm (sets are commonly 6–20 mm)	General milling. This is the default: one chuck, one set of collets, most of your tooling covered.
NT30-C20 power collet chuck	C20 power collets, roughly 6 – 20 mm	Heavy roughing where cutters pull out of ER. See C power collets — note there is no collapse range, so you buy one collet per shank.
NT30 tapping chuck	Taps, typically M6 – M20	Rigid tapping on a machine without a synchronous spindle. Axial compensation protects the tap.

Projection length varies a great deal by chuck type — around 60 mm is typical for a collet chuck, while a tapping chuck with axial compensation was listed at 86 mm reach. Check the projection before you buy; it eats directly into your Z-axis clearance.

NT belongs to the manual-change family

If your machine is changed by hand with a drawbar, you are in one of three systems, and none of them uses a pull stud:

R8 — Bridgeport-style knee mills. Drawbar thread 7/16"-20 UNF, one collet per size, not a 7:24 taper.
Morse taper — drill presses, tailstocks, older spindles. Held by friction, removed with a drift key; MTB variants add a drawbar thread.
NT30 / NT40 — conventional milling machines. 7:24 taper, keyway drive, drawbar retention.

Recognising which of the three you have is faster than measuring: if the tooling is a slim collet with a key slot and a 7/16" thread it is R8; if it has a flat tang it is Morse; if it is a 7:24 holder with a threaded tail and no pull stud it is NT.

Identifying an NT30 spindle

Look at the back of the holder, not the front. A threaded hole in the tail and no pull stud = NT.
Check for drive keys. No slots on the flange and a keyway in the bore points to an NT-style tang-driven spindle. Four slots 90° apart points to BT.
Measure the gauge diameter at the mouth of the taper — 31.75 mm confirms a 30 taper.
Thread-check the drawbar before ordering anything. See the drawbar thread table above.

Used machines sometimes turn up with mixed parts — an NT spindle with a BT-flanged holder jammed in, or the wrong drawbar fitted by a previous owner. Trust the thread you measure over any label on the machine. For the full taper comparison see tool holder tapers compared.