I just scored a deal on a barely used Powermatic 3520B that is 3yrs old for $2500. These were found in the storage compartment on the tailstock. Unfortunately I can't ask the previous owner as he passed away shortly after buying the lathe. His father who sold me the lathe had no idea what they are for as he's a flat woodworker not a turner.

They measure about 7" long overall and the shafts are straight not morse taper. The shafts are 3/4" and the heads are just slightly under 1". As you can see the "spur drive" has four holes about 1/4" diameter and 1/4" deep. the "dead center" has a flat area factory milled along the whole length.



Thanks
Ricc

spur drive_live ctr.jpg