hi, here are 2 types of transit plugs used by manufacturers of shells etc being sent to Priddy's Hard naval ordnance factory, Gosport. The larger type has no date but is marked '10LB I.E D.H.B' the thread size matches that on a No.257 fuze. The other type has no markings, is threaded on the inside and has either a red or blue ring at the top and a small hole in the bottom. Not a lot to go on I know, but does anyone have any thoughts?