This is a faithful reproduction of the straight through union fitted to SOHC (and DOHC) cambox's for connecting the cambox oil feed pipe (fitted at top of crankcase and cambox), but also used as a front crankcase breather on many Inters and magnesium racing engines. Finally it is also fitted as a breather union on the bevel chamber of magnesium racing crankcases behind the inner timing cover (while Inter crankcases instead employ a pressure telltale unit).
It has been copied from an original item fitted to an unrestored an original pre-war racing (magnesium) cambox - the union looking like it had never been removed, so I am confident it as was as original fitment from Norton's.
This union has a flat end on the side that screws into the cambox and a taper on the end that the oil pipe fits onto. It also has a slight chamfer on the side that screws into the cambox, just as the original does (I always fits either a red fibre or copper washer on the end that screws into the cambox/crankcase, to avoid marking the alloy - see item 0249).
Sorry these are not cheap, but unlike modern BSP union's (normally mass produced using AF hex and a modern tinted cadmium finish), these are CNC machined in small batch's from brass and use the correct Whitworth hexagon size
Note: I have seen these unions in both brass and dull nickel plated (often brass being fitted to pre-war engines). These are brass finish, which I think looks better, but I may be having some dull nickel plated in the near future. Email Sales@racingvincent.co.uk if you want an update on these