Two-part cross belt badges

[PeterMc]

Can anyone enlighten me on cross belt/shoulder plate badges made of a two-part construction? I am posting this in a general military enquiries section as there may be some cross-over here, although the specific badge in question is constabulary.

The following is a shoulder plate badge made of a white metal upper (with brass harp affixed to centre); but the upper is affixed to a brass lower part made from the same die. The edges have been chamfered to fit exactly. I have seen this construction in other (in fact all) badges of this particular pattern and period of the Irish Constabulary.

My questions are: (a) is this construction replicated in any other military badge examples and (B) what would be the reasoning behind doing this?