A cutting instrument used in craft, construction, and just about any other situation in which a safe method of cutting three to five millimetres of sheet stock is useful.
Widely cloned, a Stanley knife is approximately fifteen centimetres long, has a ridged slider on the top surface, by whose operation a triangular section of blade can be made to protrude from one end and lock in place. Stanley blades are extremely sharp and are double ended, being trapezoidal in shape.
As well as using reversible blades, there is a storage space for spare blades inside the handle, which is constructed of two die-cast sections of steel secured together with a single large screw.
The finesse in the design of the Stanley knife is considerable. The weight is just right, the grip is remarkably comfortable, and careful choice of screw holding the two halves together means that there's no need to carry a screwdriver to change blades, as it can be opened using a coin.
As the blade can be locked both in the stowed and deployed positions, the Stanley knife can be safely carried in a toolbelt or pocket. Almost every DIYer, handyman, roadie, electrician, plumber, vet and monkey spanker has one in their toolkit.