The phone holder is compatible with 2.3-3.3" (58 - 85 mm) wide phones and connects to the Magic Suction Cup base through the S size (3") Super Knuckle Arm. The ball head on either end of the arm allows users to freely adjust the phone's angle and can be locked into position by tightening the central knob. The Super Knuckle Arm is equipped with a hex stud that can be inserted into the built-in female socket of the Magic Suction Cup. This 6" suction cup provides a strong but removable grip on most flat nonporous surfaces, such as glass and metal. To attach the suction cup, pump the plunger until the red line is hidden. To remove the suction cup, simply pull the rubber tab at the edge of the suction cup to break the vacuum. The user-friendly suction cup is easily secured and removed efficiently from any nonporous flat surface. This set is an ideal solution to temporarily mounting a phone within a flexible 3" (7.6 cm) radius to a nonporous flat surface.