I'm trying to write a short post about hand spinners, and one of the problems I have with a hand spinner is that it hits the curve between the index finger and thumb. I can't seem to find any good diagrams with terms for parts of the hand which aren't entirely populated by medical terms, so currently my options are "curve where index finger and thumb meet" and "adductor pollicis" to describe this part of the hand.
Is there a layman's term for that part of the hand?