I used gate hinges because they are strong (built to hold heavy gates), durable (nylon bushings and powder-coated), secure (fixed pin design), and black (to match the color scheme). Readily available anywhere (HD, Lowes, TSC, internet, hardware stores, etc.) if ever a replacement is needed.

- gate hinge-fixed pin, nylon bushings, powder-coated.jpg (29.84 KiB) Viewed 8397 times
Here is part of a post I made outlining my reasoning for the choice of these heavy-duty hinges :
working on it wrote:... I'm a shadetree mechanic looking to make my own innovations, just to see what'll work and not, function not form. In defense of my solid one-piece doors: If you spread the loads caused by the act of closing/sealing the doors, and waterproof them, then future problems should be nil. Though my cut-out doors are of non-standard shape, I endeavored to spread the loads/forces involved for a tight, even seal all around. I spent some time figuring the most well-distributed loading points before I added the hinges. I did the same figuring the optimal placement for the dual-locks.

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I used three heavy duty gate hinges with nylon bushings, and bolted them on. There will be no sag, considering the light weight of the doors. The slide-locks were chosen for security and to further spread the load. Sealed high and low, the doors are held firmly against the routed interior framework and automotive door-seal. I keep them tightly shut at all times; can't warp if they're held flat!....
Overkill, yes. But I doubt they'll ever get "loose" or wear out. I even used three more to hang my vertical hatch.

- triple hinged hatch.jpg (45.34 KiB) Viewed 8397 times