After looking at the most recent build pics of the Larken shop, I have found what appears to be the X and Y lead screw nut part number. There is a bag of the nuts with Kerk part numbers on them.
ZBX-ANR-050-0333-8200
ZBX - anti-backlash style
A - Triangular Flange Mount
N - No lubricant
R - Right Hand thread
050 - Lead Screw Diameter - 1/2"
0333 - Lead Screw Pitch - 0.333"
8200 - Not sure - I think it is a customer assigned number to make ordering easier for Larken