what is this please?

hi there all, I've had this sat on my trinket shelf for about 10 years now after finding it washed up on the beach at spurn point. its only about 4" across and has at some point been squashed as far as I can tell. The nipple on the top is on a fitting that has a hexagon thread that is now more oval then hexagon and either side of this are two threaded bolts that go through the top.
on the side there are what's left of the words **PPING and TRA*** and there is a little arrow pointing to the **PPING, both of these words have what looks like white paint in them.
Its made of some light alloy from what I can tell as its not very heavy and non magnetic.
many thanks for looking.

Hi Terence./I've no idea what it is but if no one else comes up with an answer, I suggest you try the Flypast Historical Forum. There are some very knowledgeable people on there and washed up relics like yours are often identified.
Dave S