An early 1800s small sailors seam rubber. The faceted handle has initials S. I on the top.
It measures 9.5cm l x 3cm d 
Prior to the mid 1800’s the commercial sailing boats powered by wind had a vast and elaborate system of canvas sails made from hemp and flax fibre. Hemp was able to withstand salt water and the forces of the oceans. Flax canvas was made from double weave to withstand rough usage. The seams in the sails had lines of waxed stitches which had to be pressed and rubbed into the canvas using sailmaker’s liners or rubbers, usually having V shaped sides or ends.
Antique treen sailmaker’s liners or presses were made from one piece of wood usually a hard dense wood like lignum vitae. Sailors used to make their own tools and can be found with hearts, knots, initials.