The Manfrotto 131D Side Arm mounts on the center post of tripods with a 3/8" thread. It allows easy shooting straight down to the ground without having to get the tripod column and legs into the picture. Double-sided screws (1/4-20" on one side, 3/8" on other) enable cameras to be mounted on either or both ends. Length 23.6" (60cm) Weight 2.6 lbs (1.2kg)