This is a set of double nuts for the X and Y leadscrews on Shoptask and Shopmaster machines.
The nuts can be adjusted to remove backlash by moving eacu nut away from the other and giving contact on both the leading and trailing edges of the lead screw threads. They are a great upgrad for older Shoptask machines that had only a single nut.
Lather machines used these dual nuts as standrad equipment, so the set is an exact replacement for machines with a lot of wear.
One set of nuts is left hand thread and the other is right hand.