The Scotty 139 Phone Holder is legitimately a marine-grade phone holder. Varying temperatures, constant UV exposure, and saltwater is no match for the engineering-grade materials that Scotty is famous for. Offering strength, durability, and longevity, the 139 Phone Holder is made to withstand heavy use in harsh environments. Positioning and securing your device has never been more effortless and reliable with an easy-grip knob that allows for width adjustments, securing devices between 2-3/4" and 3-3/4" wide. The opening below allows access for charging your device while in use. Includes post, track, and rail mount (7/8" - 1-1/4").• Compatible with devices and smartphones between 2-3/4" and 3-3/4" wide• Dual ball-joints provide infinite flexibility for positioning• Post mount fits all Scotty post mounting options• Easy Grip-T knob Secures devices between 2-3/4"" & 3-3/4"" wide Allows access for charging your device while in use Includes post, track, & 7/8"" - 1-1/4"" rail mount