thread pitch/bolt size

[mongrel66]

i was recently trying to find the elusive 1/4"/28 pitch bolt for an ar15 and the thought came to me...why oh why do military weapons m16, m40, etc have such non available thread pitch bolt size combinations? is there any way around this dilema? i went to five hardware stores before i got the name of a private vendor that specializes in machine screws..whats the story...have they never heard of the metric system?

 

[James K]

It is not just military arms. Did you ever try buying S&W sideplate screws from anyone but S&W?

Arms makers began the whole industrial process in this country and made up their own sizes as required to meet the need to be proof against vibration, etc. Before standards were ever set, most gun makers made their own screws, so there were often as many sizes as there were companies.

In fact, 1/4 x 28 is National Fine and one of the more common American thread sizes. I didn't know it was "elusive" except maybe at the most ill-stocked hardware stores.

The trend to metric is ongoing, but mostly in international companies (e.g., GM). Small companies may be a while getting on board. The metric thread system, incidentally, is not clean and neat either. Thread pitch is only part of the story - thread angle and shape is the other, and metric stuff is all over the map.

Jim