what does this thread designator mean?

Grant Erwin · 2005-07-01T21:01:18+00:00

My sister fabricates lighting fixtures. She does a lot of threading of brass and steel tube with "1/8 straight" threads, which are apparently used a lot in lamps. I've been collecting Ridgid pipe threader stuff lately, and it looks like I'm going to have a left over 00-R ratcheting head & handle, and I thought I'd see if a 1/8" pipe die head could have its 1/8" NPT dies replaced with the correct thread for lamp work. I see Ridgid part no. 37945 is close, replacement 1/8" dies, but they call out the thread as "NPSM". They are expensive ($40+) and I don't want to take a flyer on the wrong thing. Anyone know what "NPSM" means exactly? Anyone know if this is the exact thread used commonly throughout lighting fixtures?I'd love to visit her shop and not hear her swearing at her pipe threading setup any more!Grant ErwinKirkland, Washington