You can scale the four arms by turning the adjustment knob on the back of the mount. Behind the adjustment knob is a lock knob. You need to loosen it before adjusting the arms and tighten it after finishing adjustment. Adjustable phone arms make this bicycle mount compatible with all smartphones of 3.5 to 7 inches & less than 0.48" thick. Phone thickness and stick it on the mount to better protect your phone. This cell phone handlebar mount has three removable inner pads, suitable for handlebar whose diameter is between 0.88inch and 1.4inch. The four-groove end can better fix the phone and prevent it from sliding out the bike phone mount.