This is a long breather pipe and 1/4" BSP union nut to fit breather union of type fitted to the front of drive side crankcase (i.e. union is on the left side) - most commonly fitted to magnesium M30 (and early pre-Featherbed Manx) crankcases (although can also be fitted to aluminium crankcases if they have similar front breather union fitted - as they sometimes did).
As the Norton Spare Parts Catalog of the 1930's/40's never showed pictures of the magnesium crankcases, it is difficult to confirm for sure if this type of long breather was listed - but I have copied it from a version I have seen on a friends very original 1940's pre-featherbed Manx engine - and I think it looks very period and proper.
In addition, as with other breather pipes we sell - we also supply a seperate 12"/300mm length of stainless steel lockwire,so you can attach 5/8" bore black rubber breather pipe (sold seperately)
These pipes are made from good quality copper and then nickel plated to give an excellent satin finish very similar to the original.
Fitting this breather pipe (and black rubber oil pipe if you wish to do so) adds that finishing touch of originality to your motorcycle - as well as re-directing your engine mist away from the engine onto the road or a catch-tank
Note: can also be fitted to aluminium International crankcases if they have a breather union in the same place