From the PM-1228VF-LB Manual:
This is done by “translating” the leadscrew drive, running it slower than
for US threads by the factor 86T/91T = 0.945. To see how this works,
compare the US setup for 8 TPI (0.125” pitch) with the metric setup
for 3 mm pitch. Both use the same 60T upper gear and the same C2
gearbox setting, but the leadscrew turns more slowly — so 0.125“ becomes 0.125 x 0.945 = 0.1181” = 3 mm.