Mystery Back Plates Maybe 2-3/16-10 Hardinge?

[G-ManBart]

My recent lathe purchase came with extra chucks and two have back plates that have me confused. Initially I thought they were 2-1/4-8 until I looked closely.

Using decent snap gauges and a good micrometer I got 2.069" minor diameter of the threaded section and 2.202" on the unthreaded surface. Both chucks gave me exactly the same numbers. I checked the thread and 10TPI fit perfectly. I went through metric just in case and 2.5 metric was very, very close to the same fit as 10TPI but I thought I could see a tiny bit of difference.

I'm guessing these might be the 2-3/16-10 thread Hardinge used on some lathes and other accessories, but there isn't much info out there on the specs. I will note that the place these came from was absolutely full of Hardinge stuff, so it sort of makes sense. The chucks that were on them were both marked Germany, had a triangle logo and are really, really nice. The larger plate is just under 9" and the smaller one is just over 8". If I'm reasonably sure what they are I plan on selling them cheap to somewhat cover new back plates so I can use the chucks on my 14" Logan.

 

[Leslie Sapp]

Might they be 2 1/4" x 10?
I have a Kempsmith dividing head with that thread on the spindle.

 

[G-ManBart]

Might they be 2 1/4" x 10?
I have a Kempsmith dividing head with that thread on the spindle.

I couldn't find published specs for 2-1/4-10, but I did find 2-1/4-12 and the minor diameter listed is 2.16 to 2.178" so a fair amount larger. Also, if you look at the plate on the left the smooth register surface is closer to the headstock so it has to pass over the threaded spindle and that area is only 2.202" OD so it can't pass over a 2.25" spindle.

 

[Dataporter]

Do you still have these ?

 

[G-ManBart]

Do you still have these ?

Sorry, no I sold them.