Here we have a truly massive specimen!
This clasp knife (or penny knife, jack knife, folder, etc) was the kind carried in the 18th c. and earlier by both sailors, soldiers, frontiersmen, explorers, etc for centuries. They were primarily a tool, but could easily be used as a weapon in a pinch (Spanish Albecete clasp knives in particular, which ranged in size up to truly lethal lengths and were often associated with deadly knife dueling!).
This specimen measures 4" closed, with the blade measuring just under 3". For similar examples, please see Neumann's 'Swords and Blades of the American Revolution', Gilkerson's 'Boarders Away', and Wilbur's 'Pirates & Patriots of the American Revolution'. Gilkerson, in particular, brings up that these tiny knives were sometimes used in violent mutinies and killings aboard ships. For the most part, they were tools used to splice rope, whittle scrimshaw or other similar functions. One will note this one has a 'spike' tool as well, which could also have many uses (perhaps cleaning out congealed powder or dirt from a flintlock pan.)
The construction on these early pieces were very simple, with a pin contruction holding the two pieces of fluted horn grip together. Note the fancy 6-sided finial, which I suppose is just decorative? In comparison, I've included a British naval fighting dirk with, ahem, 'bone grips', also in a fluted pattern.