New-Old-Stock from an outdoor store that has closed. This part is not documented and we know very little about it.

This is a G Jet, for an unknown brand of camp stove, to be used as a replacement Jet for a Gasoline fuel stove.

This jet has the letter G stamped in the top. Please take a very careful look at your original jet.
Look for a slot on the top for a screw driver. Look for a tiny brass filter screen on the under side.
Look for the letter G stamped in the top (G = Gasoline = Petrol = White Fuel).

The thread type seems similar to M10-1.5 or 3/8-24.