A thread file is a 4 sided file that has the common thread & pitch for both metric and SAE threads (4 of each at each end). Should be able to locate one at any reputable tool supply or parts house. I think I paid a whopping $6 or so 25 years ago. Don't need it too often but sure is nice to have on hand.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.