Forearm Wrist Link
This is the elbow-to-wrist link of the 'SG90 Four-Axis Desktop Robot Arm' kit. It is a flat bar 5 mm thick and 18 mm wide, 83 mm long from the elbow axis to its rounded tip. The Ø26 × 6 mm elbow hub screws to an SG90 double-arm horn. The horn sits in a 7.5 × 36 × 1.8 mm pocket that has a short rear lobe so the slot is fully walled, with a Ø5.3 hole for the horn screw. The flat wrist end carries the gripper palm on two M3 bolts through Ø3.4 holes 15 mm apart, at 60 and 75 mm from the elbow axis. Their M3 nuts sit in 5.7 mm captured hex pockets on the underside.
robotics kit robot-arm sg90