Inboard end for 45 mm racing boom - Optiparts owns several moulds for producing custom end fittings. All boom end fittings are made of high quality glass fibre filled nylon. The fittings below are used on Optiparts school and racing spars but they can also be used as replacement for several other school and racing spars. Unlike inboard boom-end fittings from other manufacturers ours have a firm grip around the mast.This ensures that mast and boom always turn together Diameters given are outside tube diameters.