Seperating butterfly hinges (set as pictured)
A New Zealand Jetboat favourite!
We use these a lot on jet boat engine hatches and also cupboard and hatch units that you have to remove to gain access around engines and the like.
These are now done in stainless steel.
They are pretty much square 52mm x 56mm - the 56mm side is the side with the three holes.
Price is for a paired set (2 hinges, 4 parts) as pictured.