Colt Canada’s Receiver Extension Nut – used on the UKSF issued L119A1 and L119A2 – is a classic design, which has largely been superseded in the AR market by the ubiquitous ‘castle nut’.

Prior to the introduction of the castle nut, Colt Canada style nuts were used on all US manufactured Colt AR15s between 1965 and 1992 (according to Nordic Marksman).

The Colt Canada item is distinctive. It’s shorter than the modern Colt receiver extension nut. It also exhibits cylindrical torquing notches (the holes in the side). The Colt item, on the other hand, exhibits characteristic turret-like torquing notches – which gives it the ‘castle nut’ name.

A point to note is that Colt Canada has retained the old style nut, as stipulated by the Canadian military. It’s been said that its altogether smooth nature presents less of a snagging hazard than the sharp, turreted, castle nut (e.g. when CBRN equipment is worn).

For this reason, the threaded portion of the Colt Canada buffer tube is also shorter.

Now, given that HAO is moving irrevocably towards issuing an L119A2 full kit for PTW, they’ve been busy making all the definitive L119A2 components – of which the HAO Colt Canada style receiver extension nut is one.

Needless to say, HAO’s version is RS spec.

They’ve actually made two versions: one with three staking notches and one with four. Both types are, apparently, in circulation – so I guess they are just covering themselves. Staking refers to a way of securing the nuts to prevent loosening.

The pics below are a mixture of HAO and RS Colt Canada nuts. The buffer tube is also RS Colt Canada.

More articles relating to the L119A2:

  • The original L119A2 primer, here
  • GG&G AR15 vertical fore-grip in use here
  • Magpul QDM and ASAP QD in use here
  • 15.7″ L119A2 upper in use here
  • Surefire FA556SA Suppressor here
  • GG&G Aimpoint T1 mount in use here
  • Magpul MS3 sling in use here
  • Magpul ACS stock in use here
  • Colt Canada parts – as used on the L119A2 – here
  • Manta Very Low Profile Rail Covers as used on the L119A2 here
  • UKSF Newcastle raid pics part 1
  • UKSF Newcastle raid pics part 2
  • UKSF Nairobi Kenya incident L119A2 parts breakdown here
  • UKSF Belize ‘Jungle Set-up’ L119A2 parts breakdown here
  • Confirmation bias (and the HSP Thorntail offset light mount) here