A utility knife (also known by various other names) is a cutting tool used in various trades and crafts for a variety of purposes.Zinc alloy knife Now there are more and more design,as follow:

Such a knife generally consists of a simple and cheap holder, Hobby knife set typically flat, approximately one inch (25 mm) wide and three to four inches (75 to 100 mm) long, and typically made of either metal or plastic. Some use standard razor blades, others specialised double-ended blades as in the illustration. The user can manually adjust how far the blade extends from the handle, so that for example the knife can be used to cut the tape sealing a package without damaging the contents of the package. When the blade becomes dull, it can be quickly reversed or switched for a new one. Spare or used blades are stored in the hollow handle of some models, and can be accessed by removing a screw and opening the handle. Other models feature a quick-change mechanism that allows replacing the blade without tools, as well as a flip-out blade storage tray.

The blades for a utility knife come in both double and single ended versions, and are interchangeable with many, but not all of the later copies. Specialised blades also exist for cutting string, linoleum and other purposes. Spare or used blades may be stored in the handle in some models.

 
Disassembled utility knife, blade partly extendedAnother style is a snap-off utility knife that contains a long, segmented blade that slides out from it. As the endmost edge becomes dull, it can be snapped off from the rest of the blade, exposing the next section, which is sharp and ready for use, increasing safety. When all the individual segments are used, it is thrown away or a replacement blade is inserted. This design was introduced by Japanese manufacturer Olfa Corporation in 1956 as the world's first snap-off blade and was inspired from analyzing the sharp cutting edge produced when glass is broken and how pieces of a chocolate bar break into segments.

 
Segmented blade or "snap-off blade" utility knifeFixed blade versions, usually about the size of a pencil, are widely used for handcrafts and model making and are best suited for cutting thin, lightweight materials.

Light-duty utility knife for handcrafts and model making. X-Acto No. 1 knife depicted, fitted with X-Acto No. 11 blade.A style that is often used for the cutting of boxes consists of a simple sleeve around a rectangular handle into which single-edge razor blades can be inserted. The sleeve slides up and down on the handle, holding the blade in place during use and covering the blade when not in use. The blade holder is designed to expose just enough edge to cut through one layer of corrugated fiberboard, to minimise chances of damaging contents of cardboard boxes.