not Myford as that's 12 tpi but could be Boxford

Smart & Brown used I & 3/4" by 8 tpi on the spindle nose of the Model L series plain turning lathes.

Often configured as bench top capstan and second operation machines which would commonly use collet work holding.

Clive

Measure the thread on the end of the collet, if it is 0.902" x 24 tpi W is will be the 2804 type used on the Smart & Brown model A and some model M's and L's.

Your collet threads would seem to be much smaller, but the closer looks exactly like the model A one we have.

Edited By old mart on 06/08/2022 21:24:29

It looks like somebody had a set of the collets and made a closer with the correct angle to enable them to be used on a Smart & Brown lathe. A drawbar to suit the spindle and collet threads together with an adaptor to fit in the spindle to keep the collets centralised. The closer would not be guaranteed to keep the collets aligned on its own.

It looks like a Bell Chuck, often used by the clock making fraternity..

I have both internal and external varieties, which are pulled back onto a taper to either close or expand the work holder.

In my case, the closer and expander had external 26 tpi Britsih Standard Brass threads, so adaptors mhad to be made so that a 3/8 BSW drawbar would do the pulling to close / open.

Not being a clock maker, my heretical misuse for them is making / modifying / thinning washers!

Howard.