[TR] How to tell the size of bolt or setscrew from the part number

[Chris Kantarjiev]

You're on the right track, but not quite right.

The first time I saw this system explained was in TRF's TR250 manual.

HU is a "set screw" - fully threaded.
HB is a "bolt" - partially threaded.
HN is a nut.
JF is a jam nut (thin)
LN is a slotted nut (castle nut)
TN is a thin nyloc nut
YN is a thick nyloc nut
WL is a split lock washer
WP is a plain (flat) washer

By default, it's grade 5 hardware. Bolts that have part numbers outside 
this system are special in some way - stronger, or have a shoulder, or 
an unusually threaded section. For example, the bolts that connect drive 
shaft flanges are not in this system (and I prefer to use AN hardware 
for them, but that's a different discussion).

For bolts, the first digit indicates the *wrench* size, and the 
second/third digit indicated the length in 1/16" increments. So HU704 
takes a 7/16 wrench (so it's a 1/4" bolt) and is 1/2" long.

For nuts, the last two digit indicates the wrench size.

For washers, the last two digits indicates the wrench size of the 
associated through bolt/nut.