I had the need to extend my Dobot Magician grippers by 22mm so I used Fusion 360 to model around the gripper to create this slip on extension.

To install the extensions use an allen key to unscrew the gripper arms. Move the 2 washers that connect the arm from one end to the other and screw the extenders back on.

I also included a "Sock" that can be printed in flexible filament to aid in "grippyness".