Huntsman's Friend (3.5e Equipment)
From D&D Wiki
A slim but well constructed weapon; built in such a way, that when the backs of its' two comprising daggers are brought together, the jagged teeth along the back will act as a "zip", locking the two weapons together. One blade is raised above the other, and released, the weight of the weapon pulling it down into a snug fit with its' brother. Once the two have been allowed to clip together, they act and function much like a long sword. Each blade is ever so slightly curved, so as to expose as much of the back of the blade as possible, to the make the use of its' second function easier. When the two sets of sets of teeth are set against each other, they can be struck to produce sparks akin to that of a flint and steel. In fact, each pair of these daggers are crafted to have opposing teeth sets, one of flint, and the other of the same metal at the blade.
Due to the weapons nature, the player wielding these weapons may act as if they have the "Quickdraw" feat, when switching between its' split form, and its' long sword form. When split into daggers, the player may take advantage of all perks of the weapon type therein (such as the ability to throw either weapon). Though of course, both weapons must be held to retrieve its' lengthened form.
Other than this, the weapon (or weapons) function identically to there standard counterparts; aside from the difference in price, and the "Quickdraw"-esque ability, they remain a carbon copy of their more normal selves.