BT40 and BBT40 tool holders: the difference
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BT40 and BBT40 holders look almost the same and share the same 7:24 taper. The difference is how they sit in the spindle.
What is different
- BT40: the taper touches the spindle. There is a small gap between the holder flange and the spindle face.
- BBT40: the dual-contact version. The taper and the flange face both touch the spindle at the same time, which adds rigidity.
| BT40 | BBT40 | |
|---|---|---|
| Taper | 7:24 | 7:24 |
| Contact with spindle | Taper only | Taper and flange face |
| Spindle needed for full benefit | Standard BT | Dual-contact spindle |
| Balancing in our listings | G6.3 at 15000 rpm | G2.5 at 25000 rpm |
What to check on your machine
- Is the spindle a BT40 taper? Check the machine manual or the nameplate.
- Is it a dual-contact spindle? Ask the machine maker if the manual does not say.
- What is the maximum spindle speed? Compare it with the balancing figure on the listing.
A BBT holder can be used in a standard BT spindle, but you then get no double-sided contact. A standard BT holder also works in a dual-contact spindle, again without the dual-contact benefit. So buying the wrong one does not stop the machine working, but you may pay for something you cannot use.
Which should I buy?
- Standard BT40 spindle: BT40 holders, such as the BT-40 ER-32 collet chuck, do the job and are the match for your machine.
- Dual-contact spindle: BBT40 holders, such as the BBT-40 ER-32 collet chuck, are the ones that use it.
- High spindle speeds: check the balancing grade. Our listings state G2.5 at 25000 rpm for BBT40 chucks and G6.3 at 15000 rpm for BT40 chucks.
Whichever you choose, the pull stud must suit your machine too. We list BT40 pull studs in 45, 60 and 90 degree versions.