Gripper Thumb Terminal Device

The Gripper Thumb TD is an experimental terminal device for upper limb amputees that looks like a passive cosmetic prosthesis, but it performs two-handed tasks without a Bowden cable. Since the 3D-printed device is still experimental, it should not be used without the clinical supervision of a Certified Prosthetist or Occupational Therapist. Special care should be taken in selecting the printing materials to ensure that there are no layer adhesion issues or other durability concerns.

The advantage over most other body-powered terminal devices is that the Gripper Thumb TD allows the user to grasp and release objects using the unaffected hand rather than a Bowden cable. Pressing an object against the frictional surface of the thumb tip can force the thumb to be pulled away from the fingers for an object to be gripped. Tasks with small objects (such as taking the nut off of a machine screw) or with large objects (such as opening and closing a jar, tube, or bottle) can be undertaken this way.

After placing an object in the grasp of the Gripper Thumb TD, the unaffected hand can then be used to manipulate other objects, such as putting toothpaste onto a toothbrush or cutting food with a knife while holding the item steady with a fork held in the Gripper Thumb TD.

Another advantage over the traditional split hook is that the Gripper Thumb TD is considered by some people to be more attractive.

The gripping is provided by force from a latex band, so it should not be used by people with allergies to such materials.

The Gripper Thumb TD can be washed with ordinary hand-washing and drying procedures, and it can even be sanitized in a dishwasher when fabricated of materials that can withstand that process.

The device is attached to the prosthesis with the bolt thread that is standard for th region (1/2 - 20 in the US, M12 fine-thread in most other places), and it can be easily exchanged with other terminal devices although the Bowden cable will not be used, and it can be removed or temporarily held out of the way with a rubber band.

The thumb pivots on a 6-32 (or M3) machine screw and a pair of similar screws hold the hex bolt in place on the device. A flat washer is held in place on the bolt with the same type of rubber ring that is used to provide the grasping force. Between the flat washer and the prosthesis, the ring also provides frictional force that allows the Gripper Thumb TD to be rotated for pronation or supination by the unaffected hand, but holds the TD steady in the chosen orientation.

The elastic ring is easily connected to the palm and to the thumb by a pair of zip-ties without tools (although a vise and pliers might be useful for one-handed assembly), and it can be easily replaced by clipping the zip-ties. It should not be used by people who are allergic to latex.

Files and Resources:

STL Files: Link

Instructions: Link

Video Tutorial: Link