25mm to 17mm ball adapter material: aluminum alloy, strong and sturdy. The 25mm to 17mm ball adapter is widely used for 17mm swivel ball mount bikes, motorcycle phone mounts, navigation mounts and other electronic device mounts. 1inch(25mm) ball adapter compatible with and any B size double socket arm. 17mm ball adapter compatible with for 17mm swivel ball mounting pattern GPS mount. Colour:Black Material:aluminum alloy Package Contents: 1 * 15cm connecting rod 1 * size conversion ball head Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.