The skeleton backdoors are with fixed pin block, which can mount one camera in a fishing rod or a firearm to capture footage by using other accessoriesMade of durable lightweight ABS plasticThese two back covers have rectangular foam-rubber cushion, which have shock-proof functionCompatible with Gopro Hero3 plus and Hero 4 Sports Action Camera standard and skeleton housingsCompatible with Gopro sportsman mount as wellAllows more mounting solutionsSpecifications:Brand: OzoneCompatible with: Gopro Hero3 plus and Hero 4 Sports Action CameraMaterial: ABS plasticWeight: 100gPackage includes:2x standard backdoor mount2x skeleton backdoor mount(Two fits hero3 plus / hero4 original housing, other two fits housing that is compatible with hero3)