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 accessories Made of durable lightweight ABS plastic These two back covers have rectangular foam-rubber cushion, which have shock-proof function Compatible with Gopro Hero3 plus and Hero 4 Sports Action Camera standard and skeleton housings Compatible with Gopro sportsman mount as well Allows more mounting solutions Specifications: Brand: Ozone Compatible with: Gopro Hero3 plus and Hero 4 Sports Action Camera Material: ABS plastic Weight: 100g Package includes: 2x standard backdoor mount 2x skeleton backdoor mount (Two fits hero3 plus / hero4 original housing, other two fits housing that is compatible with hero3)