Thanks! I love reading and I think it shows in the condition of my books.:D
I made that fid quite some time ago. Been used alot for splicing and knot work. (Technically it's not a marlingspike/marlinespike/marlin spike. Marlingspikes are usually made from steel.)
It's very solidly built and has good fit and finish. Mine has a strong pull, which I like. Closed length is at 4 inches (10 cm) and blade length is 3.5 inches (9 cm).
I find the size just right for my hand. I've been carrying it everyday for more than a year now.