Confusing measurement

[Milkybars]

Given those measurements I think it's likely a 6MT to 4MT adapter.

 

[fizzy]

Bottom end matches but top end doesn't. Maybe a cut down MT6?

 

[Milkybars]

It's like the ones futher down the range as mentioned by @bR39Da the adaptors are not exact morse lengths/ size but specific to the Lathe
The top end means it sticks out and doesn't go too deep into the headstock, is my understanding

 

[Wedg1e]

It’s a custom taper Colchester/Harrison used. The angle is same as any Morse taper, it just falls between sizes

Er... Morse tapers all have slightly different angles. From my thread on the Boxford 5C collet adapter:

I suspect a lot of these lathe adapters are actually just an extension of one of the standard tapers, rather than 'special' or 'custom' pieces. In the case of the Boxie, the adapter is true 3MT SIZE internally and 3MT ANGLE externally, but further 'up the slope', as it were.

 

[Wedg1e]

I found the headstock bush as discussed .
Takes an MT4 but no idea what taper the outer is. Measures 2.25 one end and 2.12" the other. Length is 2.37" approx as measured with a vernier.View attachment 286197

Hmm, well in CAD it would look like this:

and a taper angle (from centreline) of 1.571 degrees ain't no Morse taper, boy!
Now as it happens both Boxford and Hardinge adapters seem to be 2.375" long, so let me have a play with that...
Nope, that didn't work either. I extended it 0.12mm (or .005" to you guv) but it only changed the taper angle to 1.568 degrees wrt c/l, which is still a mile off any Morse taper angle.

I tried again, using your measured length and large OD dimensions (the small end being harder to measure) with 1.4933 degrees wrt c/l, and this happened:

Can I go to bed now?

 

[dan.taylor.1]

I’ve got two

What size Brad? Not sure the triumph I'm buying has one, would you part with one?