Oil tank cap, chromed, bayonet mount. Made in UK by Ceandess, Wolverhampton, no air hole in top.Opening approximately 1 13/16in (45mm), ID beteween tabs approx 43mm, cap OD 2-1/32inch (52mm). Oil tank cap for standard fit most British machines post 1950. Perfect fit for Norton 1955 and later oil tank, See MA-O230D for cap with air hole in top.Original part numbers:18526; K12/291; NM02-535283-3216