Superb high quality UK made filler neck, cap and 'O' ring seal. The dimensions are, Cap diameter 54 mm, cap height 15 mm, overall height 56 mm. Bore 38 mm. Neck outer Dia 44.5 mm with a step 5 mm long of 40.4 mm Dia. Neck thread is M48 x 2.5. Cap thread is M48.5 x 2.5.