Amazing what the the manual does not say about converting to metric
No mention of tooth counts other than 120 which you had as a normal idler - and the changes to the input gear of the QC
No mention of CHANGES shown INSIDE QC box - like clutch position AND end cap positions
What is useful that is in the specs is that the 12 1/2 has an 8 pitch lead screw
Now, other changes shown but not explained disregarded - if you had a 127 pinned to your 120 idler that makes a ratio of 1.0583333 to one - and allows you to cut such as 3mm in the 8 tpi setting - and several others.
The reason for this is that .125" divided by 1.058333 = a lead of .11811" which is 3mm
I like the part in the instructions about DISREGARD AND DISENGAGE thread dial - and leave half nuts engaged until you are done