Set the left-hand grip to two visible knuckles
The coach places the left hand on the club first, running the grip underneath the heel pad. With the club soled on the ground, he wants to see about two knuckles of the left hand, and says two and a half is all right. Seeing one or no knuckles means the grip is too weak and the clubface will stay open through the swing; seeing three or four knuckles means it is too strong and the club will be really shut.
Channel: PorzakGolf
Watch official source at 0:36