partially threaded fasteners - is there a standard on thread length?

[rmetzger]

I've been hunting for information on any standards for partially threaded fasteners. Is there a standard dictating at what fastener length does a fastener become partially threaded by default, and if so, is the length of the threaded portion part of a standard? Any insight?

 

[btrueblood]

It varies a bit by the type of fastener, you need to consult the spec. (for example, B18.2 bolts have a min thread length of 2D + 1/4 inch, but machines screws per B18.6 have thread length of 2 inches min. threads within 2 threads of the head for smaller lengths, and the thread lengths are all over the place for socket head cap screws per B18.3). Machinery's Handbook also gives the information. This applies to ASME fastener standards, e.g. B18.1, B18.2, etc.

 

[dvd]

Structural bolts have less thread length.