Thread size is like 1/2-13 UNC (coarse). Or 1/2-20 UNF (fine). Or M5x0.8 (metric). Or 3/4-inch NPT (pipe thread).
Or BSPT - british pipe thread. Or GHT - garden hose thread (US). Or British garden hose thread. Etc.......
I've attempted to measure it, but my measurements did not correspond to any of thread charts.
I'd like still to believe that Rubberset 400 some kind of standard size, so I can get a die for it.
As a matter of fact I emailed them first - no response yet.
I have an idea - hack RasorRocks 400 (both aluminum and plastic) and make them with removable/interchangable/compatible with other Rubberiest 400.
That is the reason for my cuiriosity.