This strong, reliable mounting system uses an easy-turn friction knob to lock all joints securely into place. The arm extends to 20 1/2-inches and will clamps onto anything flat or round, including wheelchairs. The Universal Switch Mounting System withstands up to 5 pounds of force, and the price includes the mounting plate of your choice. (Large Triangular Mounting Plate pictured.) Choose your mounting plate based on your intended product: Large Triangular - 5 inch sides fits Big Red, BIGmack, and BIG Step-by-Step Small Triangular - 2.5 inch sides fits Jelly Bean, LITTLEmack, LITTLE Step-by-Step, Step-by-Step with Levels, iTalk2, and AirLink Large Rectangular - 3 x 7 inches - for larger devices Small Rectangular - 1.75 x 2.5 inches fits Jelly Beamer wireless switch, other small devices Small Circular - 2 inch diameter for Specs switch FL4SH EZ Mounting Plate - 3 x 7 inch rectangle fits FL4SH scanning communicator