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Euro mill newbie - 40 taper questions


Oct 17, 2004
Shady Cove, OR
Long time lurker, soon to be new euro mill owner.

I got rid of my last round column import mill-drill and was close to buying a new square column import bench mill, when a friend offered me a small Maho MH400 P. I'll post more on that in a separate thread, but the goal is really to clean it up into a nice, compact manual mill.

I have a lot of R8 tooling and I wasn't planning to get this mill, and I haven't even wrapped my brain around the geometry of using a euro-style mill yet, but I will.

The mill has exactly one tool holder (pics attached), so I'm starting from scratch. The manual calls out ISO40 taper, but my searches seem to indicate that Cat40 with the correct retention knob / pull stud works. Is that true? Are there differences? Can I start collecting Cat40's (not NMTB's) off eBay or others and buying retention knobs to convert them?

Or is there more to it than that?

These pull studs from MariTool look close to the one I have. Nodicor has some for other listed Maho models, that are clearly different.

I have also seen what look to be more modern "ISO40" tool holders on eBay and elsewhere that have colored plastic ends on the retention knobs. Are those similar, but not compatible? Are those retention knobs removable and able to be replaced with M16 knobs? I haven't found a source for correct looking M16 knobs, but I suppose they are out there?

My goal is to keep the hydraulic closer, so I really want to sort out what I can or can't use with this machine.

Thanks for any help and hints,


DIN2080 is the standard for these, I personally use SK40 with these studs Suit Bolt SK40 DIN2080 Interior M16 without O-Ring | eBay , tried them with couple BT40 and there are issues with releasing the tool, seems that that in the BT the stud is a tiny amount closer to the gauge line of the taper and the drawbar just doesn't have enough travel to push the tool out, but that might be due to the machine design of the drawbar or its adjustment

note that there are plenty of ebay listings calling NMBT tooling DIN2080, NMBT is missing the groove for one, and the diameter is also different
The difference between sk40(din69871) and bt40 pullstud is length.

I1 lenght in the picture is shorter in sk40 and about 3mm longer in bt40

You can use both, with correct pullstud

Thank you both for your replies.

Wow, this has been a long couple of days scouring the PM site (and others) and reading all the posts that try to clarify or summarize the similarities and differences between all the various 40 taper types.

There are a lot of them, they all seem to overlap, and some seem less defined than others...
- ISO40
- SK40
- DIN 2080
- DIN ISO 7388-1, formerly DIN 69871
- BT40
- CAT 40
...to name a few

This thread had a few pieces of good info, especially the last entry, where Arno said,

SK40 .... adding another taper to the mix
By either removing one of the spindle drive keys or grinding it down on the side facing the center, low cost Cat V-Flange tooling could be utilized instead of expensive European ones.

The Maho MH400 that I am getting has removable drive dogs / keys in both of the taper sockets. So I am thinking the easiest solution, at least here in the US, is to reduce the length of one of the dogs / keys, to allow using off-the-shelf CAT 40 tooling, with the 5/8"-11 threaded retention knobs / pull studs from MariTool.

I also found a couple posts that confirm what Hari89 said, that the retention knobs / pull studs for BT40 are 0.112" / ~2.844mm longer. So holders with 5/8"-11 thread can use the MariTool pull studs, while BT40's with M16 thread can use longer ones, which I think are like jz79's eBay link, which seems to be Franz-Singer's site.

Now that I think I have that sorted out, and I can go looking for tooling, and I can move on to the other challenges with converting the Maho for electro-manual use.

Thanks again for the helpful hints,

I spent a bit more time just trying to confirm that what appear to be the two main options... SK40 and CAT40, are the same dimensions. I can see now, at least from published drawings, that they are the same except for the pull stud threads (M16 vs. 5/8"-11).

Most of the SK40 tool holders I have found look like they have to ship from outside the US. And other than collets (like ER) they are also geared towards metric-size end mills, and B-tapers, etc.

Obviously in the US there are tons of CAT40 offerings, in both fractional and metric options.

Now I'm trying to find more details and sources for the pull studs.

Is there a name or designation for the (old style?) Maho (and Deckel?) pull studs? I have only seen the two sources:
- jz79's link to Franz-Singer's metric / SK40 pull studs
- MariTool's SAE / CAT40 pull studs

Are there other sources, specs or names for these I am not aware of?


Long ago (93") i bought my first pull studs for my FP4NC Deckel.
Tooled it up using CAT 40 holders which i am still using today....

Retention Knob Supply & Manufacturing Company, Inc. - Retention Knob Supply & Manufacturing Company, Inc.
Their supplied drawing is labeled "Retention Knob # 40 Deckel "
My sheet says i paid $26.46 ea in 5-25-93.......

This was long before Mari tool was making the same item.....
Believe the price on the "Retention Knob Supply" pull studs were a bit more expensive than the Mari ones....

Mari tool has an excellent reputation and i have used him for lots of tooling....Think i would go for what he sells...and oh by the way go CAT40 ..better choices better prices...
Cheers Ross
Thank you Ross, that is very helpful.


P.S. My father-in-law (now passed) used to be right around the corner from you, in Glen Cove. We used to spend quite a bit of time staring out over the straits there. Nice part of the bay area.