That is a Bennett std length 4 ring piston. The upper hinges are short money and readily available (look on e-bay).
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I have a couple of them in my parts box, as I converted mine to indicator hinges. If you can't find any, let me know and you can have my old ones for cost of shipping.
PS: Changing them will require a short spacer clipped between the body and lower shaft, to hold a pre-load on the internal spring. That prevents the internals from launching across the garage when upper hinge is unscrewed. Change the o-rings when in there.