After being gone for six or eight years, I'm back, but with a different e-mail address. :-)
I'm cross-posting this to rec.crafts.woodworking because the company (Rockler) sells primarily to woodworkers, but it's mainly a metalworking issue.
I purchased a box of four Rockler locking casters for a project. They are not cheap ($35), but I wanted high quality. Somehow I managed to lose one of the mounting nuts before I could install them. "No problem", I thought, "The box says that they have1/2-12 threaded studs. I'll just pick up one at the hardware store." Wrong! Nothing would fit.
As most of you realize, the standard threads for 1/2 inch nuts and bolts are either 13 per inch (coarse) or 20 (fine). 12 per inch cannot be purchased anywhere, including at the Rockler store where I purchased the casters.
After e-mailing and telephoning Rockler's Tech Support, we finally figured out that they *are* standard: British Standard Whitworth!!!! I haven't seen a new Whitworth nut or bolt since the early 1960s. The only thing wrong with these is that they are 60 degrees instead of 55.
The nice Tech Support guy at Rockler is sending me a replacement nut and promised to find out why they are using a thread that has been obsolete for 50 years.