17mm to 17mm Double Ball Head Bracket with 1/4" Screw,Compatible with Garmin GPS Mount and 17mm Equipment Mount Accessories Size: The diameter of the ball head is 17mm, and the total length is 61mm. The 17mm ball head adapter is made of aluminum alloy stainless steel CNC precision machining, Very sturdy and durable, high quality non-slip rubber, which plays a good protective role for the double ball head adapter 17mm Double Ball Adapter Extension Ball Mount.You can connect other devices with 17mm balls through this product, and freely match them according to your needs. If you want to fix the 17mm ball head adapter of the device more tightly , you can use the Double Socket Arm to clamp the ball and adjust it to a suitable angle to act as a wrench , which can easily tighten the 17mm ball head adapter .