If you are just repairing some damaged threads, a thread chase file may be a much better bet. I use them all the time and work and they can be had from ENCO for like $15 rather than an expensive die and 1 will fit both shank sizes as a file is not diameter specific only pitch specific. FWIW both shank sizes are 20 tpi.

Small Shank is 1.055"-20tpi
Large Shank is 1.120-20tpi