This device, a sailmaker’s seaming palm for the right hand, wass used by sailors to make repairs on sails, and sometimes to whip or bind the ends of ropes or sheets.
It consists of a loop of leather with a hole for the thumb to go through and, in this case, a buckle. The widest part of the leather sits across the palm of the hand and incorporates a dimpled metal plate to accommodate the blunt end of a needle like a thimble.
Sailmaker's needles are necessarily tough and big enough to take the heavy thread and the plate, held in place across the palm, is used to force the needle and thread through the tough material of the sail.
This palm is worn on the right hand and is therefore for a left-handed sailmaker. It has an inside circumference of up to 280 mm.