Lock nut and washer to hold clutch to gearbox mainshaft. Suit all Nortons from 1934 to 1975. Also AJS Matchless engine main shock absorber nut. 5/8 inch x 20tpi BSC CEIOriginal part numbers:3331; A2/372; E6254; S10862; 040373 - main axle nut3332; A2/373; E6266; 040374 - axle lock nut washer000610; STD610 - AJS Matchless engine main sprocket -shock absorber nut