We always had a yellow painted (or visibly identifiable) No4 spike and/or No9 bayonet on the in-inspectors bench that was the control sample to test for FULL interchangeability of bayonets on rifle muzzles. When the big workshop at Warminster closed there was even a length of No4 muzzle welded to a steel plate that used to overhand the edge of the examiners bench and used to test every bayonet against a rifle. Unbelieveable to recall just how thorough all of our work was