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Many bolt sizes are listed here prefixed BH, (Bolt, Hex head) the part number specifies the bolt type and size. For example bolts beginning BH1 are metric, BH2 are BSF, BH3 for BA, BH5 are UNC and bolts beginning BH6 are UNF. As follows:

1st Number denotes thread type
2nd & 3rd Denotes bolt diameter:
English units: increments 16th of an inch
Metric units: increments of 1mm, except BA where the BA size is used.
4th & 5th Indicates length:
English units: increments 8ths of an inch Metric units: increments 5mm
6th The last digit is reserved for variations and finish as follows:

0 = High tensile, (no particular suffix)
1 = BZP,
2 = Black,
3 = Chrome.
4 = Stainless Steel
5 = Non standard pitch BZP
6 = Further non standard variations
Therefore BH605131 is a 5/16" UNF x 1 5/8" bolt with BZP finish.

Cap head bolts are prefixed BC.

The benefit of this system is that all bolts can easily be identified as can a choice of bolt slightly longer or slightly shorter. In many cases Triumph used discrete part numbers and as a result there was no way of knowing what the part number would be of a bolt of a particular size required. This system allows for finding sizes easily within the range.

Stainless Steel nuts and Bolts

please be aware that stainless steel, unless it is very expensive stainless steel, does not have the same tensile strength as High Carbon High Tensile steel. Whilst we can supply any screw, nut or bolt in stainless steel, we will only supply these for general use and NOT for applications of high stress and especially where safety is critical 

A Bolt or a Screw? 

A bolt has a plain shank, and a screw is threaded all the way up. There are exceptions in the use of descriptive words that confuse the issue, a set screw for instance, is generally used to clamp machine parts and may have a very short ground shank to locate the part. As a rule though, a screw is used to screw into an object, a bolt will clamp parts with the use of a nut.

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