Victorian Helmet Plate Backing - Only Smaller?

[Faugh-A-Ballagh]

Would anyone have any idea what sort of backing plate this would be? I know virtually nothing about helmet plates, but to the best of my knowledge this is much smaller.
It measures 55mm horizontally and 75mm vertically. There is a small rectangular hole in the middle and two more holes the same size about 24mm apart, and has three screw post fittings
It has been in the family for a long time, and my father can remember it being in the house they moved into in 1950, having been left there by the previous occupant.
It is probably for something other than a helmet, perhaps a belt or something.
I would be interested to know if anyone could I/D what it may be, and if there could be some sort of centre for it, as it would be nice to pair it up with something after all this time.

Thanks in advance

John