Nuts, Bolts, and Washers

Courtesy of John Kipping Spares,
submitted by Bill Kelly,

Triumph used a system of part numbers which defines the specification of a particular nut, bolt and washer.


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! Now you’ll be able to find the right nuts, bolts and washers for your Triumph!

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