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Many of us never leave home without a folding knife. This simple tool is incredibly useful for both daily life and survival in the wilderness, so unless you're in a non-permissive environment that explicitly prevents you from carrying one, it's advisable to have one at your disposal.
However, how do you choose a specific knife to carry? That's a complex question that involves quite a few variables. Blade steel is an important consideration, since it'll determine the corrosion resistance and wear characteristics of your knife. Heat treat, edge geometry, and blade profile also affect cutting performance and durability. But for folding knives, the lock mechanism is an especially important consideration. It keeps your blade firmly in place, reducing the risk of damage to the knife's structural integrity — and your hand.
Folding knife manufacturers have engineered a variety of lock types, each with its upsides and downsides. Read on for some helpful excerpts from the Essential Guide to Lock Types by Knife Informer, published here with permission:
The back lock (or lockback) uses a lock bar pinned to the scales of the blade, pivoting in the middle, and a bent spring which presses the front of the lock bar downward. The classic Buck 110 folding knife is a good example of this mechanism.
Pros: Ambidextrous, very strong
Cons: Repeated use can lead to play in the lockup, one-handed closing is often difficult
The liner lock is simple and extremely common. It uses a section of one of the handle liners, cut out and bent to create a spring effect. This lock engages the back of the blade tang when the blade is opened. Modern versions of the design use a stop pin for added strength, and a detent ball for smoothness.
Pros: Simple, inexpensive, allows for fast opening
Cons: Not suited for heavy chopping, not ambidextrous, places user's finger in front of the blade's path when closing
The frame lock is common on higher-end knives, such as the titanium frame lock on the Zero Tolerance 0630. This mechanism is stronger than a liner lock, using a thick piece of the handle frame as the lock bar instead of a thin liner. Most frame locks include a stop pin and detent ball, but designers have made many other incremental improvements — read about them here.
Pros: Extremely strong, simple construction
Cons: Titanium-on-steel galling can cause sticky lockup if not fitted with a lockbar insert, pivot tension must be fine-tuned, not ambidextrous, places user's finger in front of the blade's path when closing
The compression lock is patented by Spyderco, and it can be thought of as an improved, inverted liner lock. It's located along the spine of the blade, and engages between the stop pin and the tang of the blade.
Pros: Stronger than a liner lock, doesn't require the user to put a finger in the blade's path, can be flipped open and shut one-handed
Cons: Requires precise tension and machining tolerances
The Axis Lock is patented by Benchmade and found on most of the company's knives, though similar mechanisms have been developed by other manufacturers. This mechanism uses a sliding steel lock bar under tension provided by two omega springs.
Pros: Ambidextrous, strong, doesn't require the user to put a finger in the blade's path, can be flipped open and shut one-handed
Cons: Complex, may be susceptible to spring breakage, requires tight tolerances
Button locks (or plunge locks) are often found on automatic knives, but they're also present on some manual folders (like the Spartan Pallas) and assisted-openers (like the Gerber US-Assist). The button lock uses a spring-loaded plunger to hold the knife open; pressing the button lines up a notch in the plunger and allows the blade to pivot.
Pros: Strong, doesn't require the user to put a finger in the blade's path, fast and easy to use
Cons: Difficult and expensive to manufacture, not ambidextrous, some jurisdictions may have laws which designate button-lock knives as switchblades
For more details on variations within these categories, tips on how to find the right knife for your needs, and information on non-locking slipjoint and friction-folding knives, check out the complete Essential Guide to Lock Types from Knife Informer.