Marlin spikes are used extensively in sailing for tying and untying knots. There is a fairly detailed section in the Ashley Book of Knots on how to use them to tie turk's head knots, there are plenty of online resources on how to use them to tighten and loosen knots. I make a variety of sizes, many of which are custom orders and don't show up on my web site. If there is a marlin spike pattern that isn't shown (baring copying another makers work) please let me know and I should be able to make on for you.
This hand machined marlin spike is made from solid grade 5 titanium bronze. It is 1/2” in diameter and 6” long. This spike features a 2 1/2” taper and a 3/16” lanyard hole.
Kydex sheaths are available elsewhere on my site at additional cost.
