This is truly a tool of a thousand uses. The thinness of its blade means it can be used for precise marking on cutoff work. The razor-sharp edge can cut through plastic, wood, and other fibers; it can be used to score soft metals. The utility knife is invalu¬able for tasks like hanging wallboard, trimming wallpaper, cutting cardboard or plastic sheets or ceiling tiles, and dozens of other jobs.
As handy as the tool is, the utility knife must be handled with respect. Its design and manufacture allow for this, as the blade retracts into the body of the tool. A flick of your thumb on the but¬ton built into the top of the case slides the blade in and out.
Given its thin, sharp edge, the blade is fragile. Since utility knife blades dull quickly and are breakable, the tool is designed to accept replacement blades easily. On the side of the case is a screw that, when loosened, allows the case to be opened. Inside is a cavity for storage of new blades, as well as the sliding mechanism that allows the blade to be withdrawn when the utility knife is not in use.
The sharp and pointed blade can also cut the user with ease, so the blade should always be retracted when it is not in use. Spare blades should be stored in a safe place, and the tool should always be stowed out of the reach of children.
This tool is sometimes referred to as a razor knife and (especially in England) as a shop knife or trimming knife. The standard blade has a straight cutting edge, but some models will accept other blades, some with hooked or curved blades. The hooked blade is especially useful for cutting linoleum because the blade is sharpened on the in¬side curve, which makes it less likely to slide out of a cut. Blades with the edge on a convex curve are useful for making cuts along lines that aren't straight, such as when cutting to match a scribed line.
One variation on the standard utility knife is a thinner, lighter model that uses a blade that is scored so that sections of it can be snapped off. With such knives, when the end of the blade dulls, the blade is advanced out of the casing, the old tip is broken off, and a fresh edge is then usable. Such models have the advantage of making a new, sharp edge available in a second, as against the disadvantage of a shorter cutting edge and, on some models, the fact that withdrawing the blade into the handle is more time-consuming than on traditional utility knives.
Snap-off blade models are best suited to uses where new blades are required very frequently; for most purposes, the traditional utility knife is easier and safer to use.