confirmed, im no mason, and this is how i shake hands. it puts you in a position of power - my grandfather (first generation immigrant, made a beautiful future for his family through hard work and never associating with riffraff) taught me this is how you shake. the finger on the inside of the wrist actually puts you biomechanically in control, effectively weakening the grip of the other. since the flexors in the hand run through the inside of the wrist, a simple finger against someone’s wrist means you dictate strength of the shake and how long it lasts. puts you in a good position for a counteroffensive, should your partner have plans to harm you. old timey tradition stuff, but it matters.