This is the oil delivery or return union that was fitted to the crankcases of pre-war OHV and Sidevalve models, then continued on the post-war OHV and Sidevalve (SV) models until approximately 1950-51 when the twin unions were replaced with a single 'cast' union junction box. These unions are CNC manufactured by us and faithfully replicate the original unions, including the correct Imperial hex spanner size.
An original brass A2/721 union (taken from a 1938-47 set of OHV crankcases, and definitely an original item from that engine) was used as the pattern to make these, and the dimensions were copied faithfully - including chamfers and differences in both ends.
Similar to the A11/721 union on SOHC crankcases and cambox's (Item 0248B), these unions have a chamfer to the hex on one end only, and that chamfer coincides with a flat end (as shown in the last photograph) - this is the end that screws into the crankcase. The other end has a taper (rather than a flat end), and this is attach the standard 1/4" BSP tapered pipe unions.
Two are required per engine (Feed and Return). Note: please check your crankcases if unsure, but from 1950 onwards, the OHV/SV engine crankcases were modified to use a single oil union block, instead of these seperate unions - see the photographs attached, and email us if unsure.