T-nut bar stock?

[Papa Charlie]

If you remove the swivel under the vice you may have sufficient room to use standard T nuts.

 

[dsclathe]

If you remove the swivel under the vice you may have sufficient room to use standard T nuts.

No swivel under vise the swivel is on plate to lathe. Vise is flush mount to vertical slide.

 

[Papa Charlie]

No swivel under vise the swivel is on plate to lathe. Vise is flush mount to vertical slide.

Didn't realize that you were trying to fasten to a lathe. Just use some flat bar that fits into the wider (bottom) slot. Based on the setup, I wouldn't worry about the smaller slot. It would be more important if you were inserting a bolt that had to deal with the blind hole against the bottom of the slot, but if you are going to extend past the edges then this would not be an issue.