s4 arm clamp

thingiverse

Bike Phone Holder designed specifically for Samsung S4, but suitable for any phone of comparable size. Two holes are pre-drilled for M5x20mm cap screws; it's recommended to use a through bolt with nut for added stability, although threading may be required. To assemble the holder, cut the ring in half along the part line. To secure your phone, attach it to a protective case and reinforce with extra-strong velcro.