Utility Knife: The Anatomy of an All-Purpose Tool

Look in any home or industrial toolbox and sooner or later you'll find a utility knife. More versatile than a hammer, this powerhouse tool is used for almost any material you can think of. Although the utility knife definition technically extends to some specialty knives such as linoleum cutters, most people use the term to mean a broader-use tool. In fact, a utility knife (also known as a box cutter, folding knife, carpet knife or pen knife) is defined by its versatility. Whereas most knife designs have specialty applications—think hunting knives or surgical scalpels—a utility knife is meant to be multipurpose.

Some typical utility knife uses include:

• Marking or scoring materials
• Opening corrugated cardboard and other packaging
• Trimming excess material off injection-molded plastics or rubber
• Cutting binding materials like packing tape, cord, twine or plastic strapping
• Scraping plastic, paint or film off smooth, hard materials like glass or metal

When you’re looking for the best multi purpose knife, you need to evaluate its design approach to effectiveness and safety. There are two ways that manufacturers address these issues: with handle design and with blade design.

Utility Knife Handles

Each type of knife has different strengths and weaknesses, so the best utility knife for the job often depends on the job itself. Most people, when they buy a utility knife, only look at its handle design. It’s important to consider blade design, too, but here is a summary of the pros and cons of common handle types.

Fixed-Position Utility Knives

Traditional style utility knife with a dangerous metal blade.

As the name suggests, these knives have a single blade that stays in the same position as you cut. They're further divided into three subgroups:

1. Replaceable: the user can replace the blade 
2. Folding: the handle folds to protect the blade (and user) when the knife isn’t in use 
3. Multiple positions: the blade remains fixed during the cut, but the user can choose between set positions to adjust the length of the blade for each job

The Slice 3-Position Manual Utility Knife with ceramic safety blade.

Strengths

• These knives tend to have strong handles. A fixed blade can generally handle more heavy-duty materials.
• If the knife has multiple blade position options, the user can adjust the blade length to the job at hand.

Weaknesses

• If the user accidentally leaves the blade exposed after cutting, there's a potential for injury. For this reason, many industrial safety officers choose retractable blades for the workplace. 
• Some of these knives do not have replaceable blades, which means you need to purchase a new knife when the blade dulls. 
• Unless the blade position is adjustable, the exposed area of the blade may be too long for the application, causing damage to materials.

Retractable Utility Knives

One of the first safety features to revolutionize utility knife handles was the retractable blade. Auto-retract knives expose their blade as long as the user holds down a button or slider. Once the slider is released, a spring-loaded mechanism automatically pulls the blade into its casing. This innovation reduces user error between cuts, no longer relying on the user to remember to retract the blade for safe storage.

The latest advance in retractable blades adds another layer of safety. In the new model of self-retracting utility knife, the blade senses when it has lost contact with the cutting material and retracts automatically, even if the user is still holding the button or slider down. This prevents accidents if the user slips while cutting.

Strengths

• Blade retraction adds a layer of safety so there will never be an exposed blade left lying around.
• A self-retracting utility knife is even safer, as it retracts whenever the blade loses contact with cutting material, even if the user has not released the button or slider.

Weaknesses

• Depending on the design, it can be cumbersome to hold down a button or slider for every cut if the knife is in heavy use.
• The retraction spring is one extra mechanism that could potentially break, rendering the knife useless.

Other handle features to consider include blade storage (some knives store replacement blades right in the handle) and knife storage. A tool is only useful if you can find it. Look for some kind of utility knife holder, lanyard hole, or other storage option.

Ergonomics are another important component of handle design. Look for evidence that the knife manufacturer has considered the ergonomic impact of its design.

Utility Knife Blades

The blades themselves are often overlooked when users evaluate knives, but what cuts you: the handle or the blade? The best utility knife blades combine safety and longevity in their materials and design.

One Slice ceramic safety blade lasts, on average, as long as 11.2 metal blades.

Traditional Metal Utility Knife Blades

Everyone is familiar with these because for a long time, they were the only option on the market. The metal used is typically a variety of steel.

Strengths

• Blades are very thin and cut very easily.
• Thinner blades can withstand a certain amount of side load by bending before they break.

Weaknesses

• Blades are very thin and cut very easily. Notice that this same point is listed as a strength. It’s considered a weakness because they cut skin very easily too, making them dangerous to handle.
• Blades dull quickly. Because metal is a relatively soft material, metal blades start out excessively sharp and quickly become dangerously dull.
• Metal has several properties that are problematic for certain industries: it rusts, it’s often coated in oil to prevent rusting, it sparks, it’s conductive, magnetic and can react to chemical agents.

Snap-Off Utility Blades

This knife has a dangerous snap-off utility blade.

These blades (which actually represent a subcategory of traditional metal utility knife blades) are originally a Japanese invention and consist of a thin razor-like blade with several scores across its width. Once the edge of the exposed blade becomes dull, the user can snap it off, revealing a new sharp edge. Each blade contains several snap-off sections, meaning the entire blade is replaced less often.

Strengths

• These use extra thin razor blades, and so are suited to scraping.
• Because each blade has several sections, you will need to buy fewer replacement blades over time, compared with other metal blades.

Weaknesses

• The snapping action that exposes a new blade is dangerous. It exposes a fresh, sharp edge while the dull section can easily fly off in an unpredictable direction, causing injuries.
• The handle of these models is not particularly strong. If stepped on or run over, the handle may break, causing injuries and exposing multiple razor-sharp sections of the blade.

Slice Ceramic Safety Blades

Although several varieties of ceramic blades exist, Slice is the first company to bring safety to ceramics with our patented finger-friendly grind.

Strengths

• Extra hard zirconia (advanced ceramics) is much stronger than steel and therefore cuts effectively an average of 11.2 times longer than a comparable steel blade. This is a huge price advantage.
• Because Slice blades have superior wear resistance, users handle them less, reducing the risk of injury.
• Slice’s patented safety grind cuts materials effectively but resists cutting skin. Slice blades are much safer to handle.

Weaknesses

• Ceramic blades don’t fare well under a side load. However, no blade should be subjected to side load (used as a screwdriver, for example), because they may break and cause an injury.
• Slice ceramic blades are not metal detectable. As such, they cannot be used in certain sectors of the food industry where detectability is required.

Utility Knife Safety

The cost of lacerations from workplace utility knives doesn’t stop with medical bills. In fact, OSHA estimates that a laceration injury costs the average company over $40 000 in direct and indirect costs. That doesn’t include costs that are difficult to quantify, such as lowered morale. No matter what tools you choose, it’s crucial to train workers how to use a utility knife properly, as well as when to use a utility knife and when to choose a specialty tool.

Safety Issues to Consider

• The bigger picture: Price vs. Cost
• How ceramics solve common safety issues
• Safety blades - what makes a blade truly safer?

When you’re trying to find who makes the best utility knife for your application, always include safety in your evaluation. After all, when a number of safer choices are available, there’s no need to settle for one or the other. Why use a utility knife that’s effective but unsafe?