[montauk]

I found a thread chaser at McMaster Carr, $75.
https://www.mcmaster.com/dies/thread-size~m30/

I also found a cheapo die on Ebay.
https://www.ebay.com/itm/391757154295?chn=ps&_trkparms=ispr%3D1&amdata=enc%3A1OSFtFDN_Q6atxZav6z8YTg17&norover=1&mkevt=1&mkrid=711-213727-13078-0&mkcid=2&itemid=391757154295&targetid=4580702891777581&device=c&mktype=&googleloc=&poi=&campaignid=418640321&mkgroupid=1233652283797640&rlsatarget=pla-4580702891777581&abcId=9300602&merchantid=51291&msclkid=b61092d9114e12251877f1f3eb9f5053

Both are large enough that I'm not sure they'll even fit between the fittings.

I'll see what I can do with a jewelers file. If I have to replace the thermostat, I think I'll drop the whole mess on the floor from the trombone back.