The adapter ring allows you to mount UV lens, gradient filter lens, polarizing lens of 58mm diameter on to the housing for GoPro Hero 3 3+ 4 Black / Silver Editions For Filter Size: 58mm - Please verify your filter thread size before order Adapter ring fits a specific style housing (the square portion has 8 screws). Made of aluminum alloy by CNC, anodized black finish, firm and durable. Compatible with GoPro Hero 3 3+ 4 Black / Silver Editions.