US mortar fuze M52 series

[MINENAZ16]

Hello,
I can't find this combination (bakelite base, aluminum top) in my doc.
It's the opposite as M52B2.
Is it an original combination (désignation ?) or a collector's thing ?

 

[US-Subs]

It is correct. Not sure of the designation, and I'm at work so cannot check the item on the shelf, but here is a poor picture of one of mine, taken from a shelf shot.