Almost identical primers on 60x64R and Bofors L/60

[Falcon]

Is there any reason why the primers on a 1917 German 60x64R case and a 1939 Royal Laboratories 30x311R Bofors L/60 case are almost identical? They are almost dimensionally identical, and the tool holes are almost identical (three equally spaced semi circular slots). However, the taper on the base of the body of the primer that is usually hidden inside the case, and the threads, are slightly different.

 

[Quatermass]

The primer No. 18 was a British manufactured version of the original AB Bofors primer used with the mark 1 case, Mk 1* & 2 cases could take either the No 18 primer or an adapter & No. 12 primer, Mk 3 & 4 cases used the British designed No.12 primer only.

I'd guess that AB Bofors used an already avalible primer as the basis for there deisgn.

Quatermass.