This may be of help:
MOD codes for fixings:
28D Bolts A.G.S.
28E Clips A.G.S.
28F Couplings A.G.S.
28FP Aircraft Fastner and Quick Release Pins
28G Eyebolts A.G.S.
28H Ferrules A.G.S.
28J Filler Caps and Fuel Filters A.G.S.
28K Fork Joints A.G.S.
28L Locknuts, Lockwashers A.G.S.
28M Nuts A.G.S.
28N A.G.S. Miscellaneous A to O
28P Pins A.G.S.
28Q Rivets A.G.S.
28R A.G.S. Miscellaneous P to R
28S Screws A.G.S. Miscellaneous A to O
28T Studs A.G.S.
28U Trunnions and Turnbuckles A.G.S.
28V Unions A.G.S.
28W Washers A.G.S.
28X Wire A.G.S.
28Y A.G.S. Miscellaneous S to Z
29A Bolts and Nuts, General Hardware
29B Screws, General Hardware
29C Eyelets, Roves, Screw Cups, Washers, General Hardware
29E Pins, Woodruff Keys, General Hardware
29F Rivets, General Hardware