Square head bolts were standard for line pole work until recently, and square nuts are still standard (required by building code in some cases) for concrete foundation work where they will be tightened up by hand wrenches. ![]() The special order option is more challenging. Today, I am able to get nuts (but there are sizes that are difficult) and some shorter bolts. At the time there were two head sizes for any bolt diameter, a normal, and "heavy head" Our West Side flat cars (built 1928-1928) have a mix of square head and hex.Īs late as 1995 square head bolts were easily available at local specialty shops in a great variety of lengths and sizes (for example, 2, 7/8x17", the bolts were made to order, with a 2 week lead time). I suspect a locomotive or similar machine used more hex earlier as well. Similarly we find hex used earlier on air brake equipment, when installed on a wood car built with square head bolts. Generally we see square head bolts used on the Carter built equipment, but, we do find some hex on passenger cars, suggesting that hex was higher class. Generally square heads are better for open end "hand" wrenches. The primary driving force was use of socket wrenches. It's intriguing that, for such a common thing as bolts and nuts, so little about their history is readily available on the web.īTW, I posted the same question on the NorCal Group. Sounds a lot like the info on the link posted on FB about how carriage bolts were made. Similar methods of manufacture were probably used prior to mechanization, though on a smaller scale and with manually operated machinery. The next step rolled the threads onto the wire shaft.įor both bolts and nuts, heat treating/hardening of the metal was the last step.īy the way.that 1949 agreement to standardize nuts and bolts into ISO inch and ISO metric was probably when the square headed bolts/nuts ended production in mass.as it would have required new investments in machinery. This resulted in some of the heads being distorted and not centered on the wire shaft. The bolts were then pushed through a form that squared the head. ![]() The wire was heated till it was soft.then put into a machine that squashed the head area to form a mushroom like head.and it also cut the bolt to length. The cutting process wasn't very accurate.and that's why cut nuts didn't always have the hole in the center of the nut. These long pieces were fed into another machine that threaded the holes.then a smaller shear cut across the "stick". Then the sheet was "cut" in a shear to create long "stick" of steel with a single row of holes. customer: full hex rivet nuts and the FLEX-5 tool. Cut nuts were made by drilling/punching a large sheet of steel with thousands of holes aligned in rows and columns. Socket head cap screw mandrel for sizes up to M12 and 1/2-20. ![]() Square headed nuts were also called cut nuts. My grandfather was the general manager of a US Steel nail and screw factory.
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