Tim,
I found this described as a mid 19 th C fid (marlinspike)
".....Measures a little over 18 inches long with a max diameter of 2 3/4. The spike weighs approx 1 3/4 lbs..."
Checking the description of the types of wood used in the construction of these 'fids' ...Lignum Vitae and other heavy dense timber species were used. The same wood used for clubs
The size of the 'fid' would be dependant on the thickness of rope it is used for.....which suggests that if yours is a fid ... the ship this was used on must have been fairly large.....