If you’ve ever looked at a parts listing for your Triumph you’ll see that nuts and bolts have cryptic part numbers like KT504 or YN2912. Whilst these look seemingly random, Triumph used a system of part numbers which defines the specification of a particular nut, bolt and washer. Hence armed with a parts book you can work out what the bolt is in plain english.
Prefix gives type of nut.
* HN refers to a plain nut.
* YN refers to a nyloc nut.
* JN refers to a jam nut (ie half thickness).
* TN refers to a thin type nyloc.
Last 2 digits give size & thread
* 03 = No. 6 UNF
* 04 = No. 8 UNF
* 05 = No. 10 UNF
* 07 = 1/4 UNF
* 08 = 5/16 UNF
* 09 = 3/8 UNF
* 10 = 7/16 UNF
* 11 = 1/2 UNF
* 12 = 9/16 UNF
* 13 = 5/8 UNF
* 53 = No. 6 UNC
* 57 = 1/4 UNC
Thus a YN2912 is a 9/16″ UNF nyloc
Prefix gives type of bolt
* HU refers to a setscrew (threaded all the way)
* HB refers to a bolt.
* KT refers to a countersunk slotted.
* KX refers to a countersunk crosshead.
* PT refers to a pan head slotted.
* PX refers to a pan head crosshead.
First digit (s) defines thread size as per nuts above, but the thread type is always UNF unless the second digit from the right is 5 in which case the thread will be UNC. The last two digits give the length in eighths of an inch (up to 49). Thus a KT504 is a No. 10 UNF, a countersunk slotted head 1/2″ screw.
Washers prefix gives type
* WP refers to a plain washer.
* WL refers to a lock washer.
* WN refers to a shakeproof washer.
The last two digits give the size as per the chart above for the nuts (03 to 13).
That’s it, as you can see it’s not too difficult to work out and now you’ll be able to find the right nuts, bolts and washers for your Triumph!