Can anyone identify this ?

I bought a job lot of aircraft books (early 1940’s) and long with them was a dial guage, a Gypsy Queen Engine plate and another plate 130mm diameter, dished , with HI or IH impressed in it.

Can anyone throw any light on what it may be off, given all the other items were aviation I am assuming this is too but I am stumped as to what it could be off.

Cheers

Clive