1/4-20 Cap Screw & Machine Screw

ASME B 18.2.1 for Cap Screws ASME B 18.6.3 for Machine Screws

ASME B 18.2.1 for Cap Screws
ASME B 18.6.3 for Machine Screws









You wouldn’t think folks would get their shorts in much of a twist over the size of the hex shaped head of a bolt. Yet, they do. The ASME sets the standards for bolts and RIGHTech has been doing everything in its power to match their standards for 45 years.

But, when we were first introducing titanium to the anodizing world in the mid 1960’s, it was new and different and as much as we wanted it to fabricate like stainless steel, it just wouldn’t cooperate. As we worked to create our own fabrication processes, convincing the bolt making world to produce our bolts was a challenge.

For a 1/4-20 bolt, ASME B18.2.1 said our heads should be 7/16 inch (.437) measured across the flat sides of the hex shaped head (see illustration). That was a struggle. Standard head forming technology that worked great on steel and stainless steel didn’t do well on titanium. The standard bolt making practice of hitting the end of a wire to push metal into a hex shaped form at speeds of up to 4,000 parts per hour was not making great, titanium heads.

So, the ASME gave us a little design flexibility. They let us design our bolt as a Hex Head machine screw ASME B18.6.3 (see illustration) with an indented head that was only 3/8 inch (.375) width across the flats (AF).

While RIGHTech Fabrications eventually solved the 7/16 titanium bolt making challenge, both head sizes have remained available in the anodizing world. The smaller head saves a bit of money and is simpler to fabricate. The larger head makes it easier to get a tighter connection and reduces the number of tools required in the shop.

So, when we’re making racks or sending our customers bolts, we always ask, “What size bolt head do you need?” Because we stock them both to be able to serve everyone.

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