This is the oil reistent paper gasket that was fitted to the newly re-designed (civilian version) Sidevalve Norton engines (i.e. 16H and Model 1 types) from 1938 until the end of 1947. Note that the WD 16H Engine which was manufactured at the same time did not have this cover fitted
In 1938 both the OHV and Side valve engines had a re-design and the Side Valve model had a newly designed barrel that included a cast in tappet adjustment area to the barrel, with an aluminium square shaped cover. This gasket is the gasket that was fitted behind that cover. Although I do not have an original barrel to show the gasket against, we have included a picture from the Norton 1939 model catalog that shows this engine, which was manufactured until the end of the 1947 model year.
Note that the WD 16H engine continued to be manufactured for WW2 army contracts alongside this model, but the WD engine was based on the pre-1938 design and did not have this gasket fitted.
These head gaskets are manufactured for us by a well established specialist UK gasket manufacturer.