A tang or shank is the back portion of the blade component of a tool where it extends into stock material or connects to a handle - as on a knife, sword, spear, arrowhead, chisel, file, coulter, pike, scythe, screwdriver, etc. One can classify various tang designs by their appearance, by the manner in which they attach to a handle, and by their length in relation to the handle.
A full tang extends the full length of the grip-portion of a handle, versus a partial tang which does not. A full tang may or may not be as wide as the handle itself, but will still run the full length of the handle.
There are a wide variety of full and partial tang designs. In perhaps the most common design in full tang knives, the handle is cut in the shape of the tang and handle scales are then fastened to the tang by means of pins, screws, bolts, metal tubing, epoxy, etc. The tang is left exposed along the belly, butt, and spine of the handle, extending both the full length and width of the handle.
Partial tang designs include stub, half, and three-quarter tangs, describing how far the tang extends into the handle of the tool. The most common partial tang design found in commercial knives is on folding knives, where the tang extends only as far as the pivot-point in the handle. Scalpels, utility razor blades, and a number of other knives are commonly designed with short partial tangs that are easy to fasten and unfasten from the handle so that dull or contaminated blades may be quickly exchanged for fresh ones, or so that one style of blade may be exchanged for another style while maintaining the same handle. Hollow-handled knives also incorporate a partial tang. Many inexpensive knives and swords designed for decorative purposes incorporate partial tangs and are not intended to be used for cutting applications.
A full tang knife or sword generally allows for increased force leveraged through the handle against the resistance of material being cut by the blade, an advantage when used against harder materials or when the blade begins to dull. A full tang also increases the amount of stock metal in the handle of the tool which can be beneficial in altering the balance point of the tool since the blade of a knife or sword is often quite heavy compared to the handle. Adding weight to the handle of a knife or sword to offset the weight of the blade moves the rotational balance point back toward the hand where it can be more easily manipulated to great effect, making for a nimble, agile tool. In general, a forward-balanced blade excels at chopping but sacrifices agility and ease of manipulation; a centre or rear-balanced blade excels at agility but sacrifices raw chopping power. Knives and swords intended for specific purposes will usually incorporate whichever design is most suited to how the tool will be handled for that specific purpose.
A partial tang knife or sword is generally not able to leverage as much force against the resistance of material being cut as a full tang design would allow. This limits the amount of force which a user should apply to the handle of such a weapon. Such designs may be optimal in light-weight knives or swords designed to be kept extremely sharp and used to cut less-resistant materials. Scalpels and Japanese samurai swords are perhaps the most well-known examples of such tools.
Most of these design styles can be used with full or partial tangs and the use of one does not exclude the use of another. For example, a sword may have a hidden, encapsulated, rat-tail tang.