I had an idea to carve multiple grips on a cube of wood, it is 70mm, just the right size for a handhold. One at a time I persuaded 6 people to grasp the block while I traced around their fingers and thumbs. Carving out search set at a time, I was able to keep the sets from overlapping too much. One grip is like that of a cricket ball, finger tips only, another held it just with thumb and forefinger, then a variety of different holds but only one left-handed. The sizes varied quite a bit too.
I wrote their names near their thumbs whilst I was carving but I might sand those off. It’s interesting that everyone found their finger holds easily if they began by finding their thumb position.