The literature on cutting metric threads on a Myford 7 Series lathe refers to the use of a 21 tooth change wheel which is now effectively extinct. I have prepared a table showing gear trains for all the ISO metric series threads in my copy of the Dormer Tap and Die Handbook using the readily-available 42 tooth change gear instead. I have attached it as a PDF.

I have not carried out a check that all these trains are immediately useable – some of the tooth counts may need massaged to fit.

This table refers to lathes without the QC gearbox.

Peter R Hastings, Skye.

Download the table here.