Convert pitch to Imperial
1.25 / 25.4=0.0492
Calc TPI
1 / 0.0492=20.32
The lead is 0.0492'', the TPI is 20.32
Major dia = 0.354''
0.866 is a constant for metric thread depth
0.866*pitch = 0.866*1.25 = 1.0825mm = 0.0426'' thread depth
0.0426*2 = 0.0852''
0.354-0.0852=0.2687''
Minor dia = 0.2687''
This should give you enough to set it up just like cutting Imperial threads.