Dimensions and taper ratios for Morse (MT0-6), R8, Brown & Sharpe, Jacobs, and V-flange CAT / BT / NMTB tool holders used on drill presses, mills, and CNC spindles.
Updated Apr 24, 20263 min read
Machine tapers transfer torque and provide self-centering. Self-holding tapers (Morse, Brown & Sharpe, Jacobs) grip on friction alone — knock-out slot and drawbar release them. Steep / self-releasing tapers (R8, CAT / BT / NMTB / HSK) need a drawbar to hold the tool and come free with a rap once the bar is loosened. Taper per foot (TPF) is the included diameter change — a 0.500 TPF means the diameter grows 0.500" over 12" of axial length (i.e., each side angles 1.19°).
Hollow taper contacts the spindle both on the 1:10 taper and the flange face — higher rigidity than CAT / BT at the same size.
vs CAT
HSK has ~2× the bending stiffness of same-size CAT / BT and zero axial pull-out. Downside: fussier on cleanliness, more expensive toolholders.
Self-holding vs self-releasing — how to tell
Self-holding tapers (Morse, B&S, Jacobs) are shallow (~3° to 8° included) and grip on friction alone — a pound of force is enough to seat them, and they need a drift punch through the knock-out slot to release.
Self-releasing tapers (R8, CAT, BT, NMTB, HSK) are steep (15-17° included). They cannot transmit torque without a drawbar and driving key / dog.
All CAT / BT / NMTB toolholders have the same 7:24 taper ratio (8°17'50") but differ in flange OD, pull-stud thread, and retention mechanism. CAT = ANSI, BT = JIS, NMTB = older ANSI (face is pin-driven; CAT / BT use keyway drive).
BT and CAT toolholders are not interchangeable despite identical tapers — flange is different, retention pull-stud thread differs, and balance grade may differ. Always match the spindle type.
To ID an unknown taper: measure small-end diameter and length with calipers, look up in the table. 2.5" length + ~0.572" small end = MT2; 0.912" length + 0.687" small end + drawbar = R8.
Notes
Dimensions per ASME B5.10 (Morse / B&S), ISO 7388 (CAT / BT), DIN 69871 (SK / BT / HSK). Commercial toolholders are typically toleranced AT-3 or AT-4 (ISO 1947).
Was this article helpful?
Cookies & ads
Tools run client-side — your inputs stay in your browser. The site is funded by Google AdSense, which uses cookies to serve ads. Choose Accept all for personalized ads, or Reject non-essential for non-personalized ads only. Privacy · Cookies
Essential StorageTheme, consent state, CSRF tokens. Required for the site to work.
Always on
PersonalizationRecently used tools, custom colors, accessibility preferences. Stored locally on your device.
AdvertisingAllow Google AdSense and its partners to use cookies for personalized ads. If off, you'll see non-personalized ads instead. Details.
AnalyticsAggregate, anonymous page-view counts so we know which tools to improve.
AI IntegrationStores your API key locally for optional AI features. Key never leaves your device.