Greyprints for fabbing a sixth (seventh, eighth, ...) finger to make pictures of you seem AI generated or manipulated.
There is an insert that can be used for people with small fingers, otherwise just pull it off and discard it. Printed with SpiderMaker SpiderFlex TPE (Matte TPU) 75A-80A (Fair Skin): https://www.amazon.com/dp/B0BY7ZHDWM
Pick an appropriate shade of TPU, of course.
Silver Ring Splint manufactures custom hand and finger splints for Ehlers-Dahlos Syndrome and arthritis. Looking at them, you can't even tell they're not exquisitely designed custom jewelry.