Spyderco byte | July/August 2025 - Edge-U-Cation®: The Evolution of the Back Lock
The oldest known folding knife is the “Hallstatt Knife,” so named because it was discovered near Hallstatt, Austria. Estimated to date back to between 600 and 500 BCE, it was made of iron and bone and featured a simple “friction folder” style of construction. Amazingly, that construction method would remain substantially unchanged for almost 2,000 years before the advent of lock-blade folding knives.Up until the late Middle Ages, the carry of swords by all classes of society was generally allowed in Europe. By the mid-18th century, however, a variety of laws had been passed limiting sword carry to members of the nobility. Other legislation restricted the production of weapons themselves and craftsmen were forced to adapt their skills to other products. This paradigm shift, along with the development of spring steel, inspired the development of large, lock-blade folding knives—most notably, the Spanish navaja.
Derived from the Latin novacula, meaning razor, the navaja originated in the Andalusian region of southern Spain in the late 1600’s. Although earlier versions of the pattern also took the form of friction folder “peasant’s knives,” the advent of spring steel paved the way for their evolution into lock-blade folders. Craftsmen added a steel backspring to the outside of the knife’s handle, anchoring it at the butt end so the front end could flex. When the knife’s blade was opened, the front edge of the spring contacted a shoulder filed into the back of the blade, stopping its opening arc. At the same time, a hole in the forward section of the backspring engaged a notch in the top of the blade tang, effectively locking the blade in the open position. Together, these opposing contact surfaces provided two of the three points necessary for the triangular geometry of a folding knife lock mechanism. The blade’s pivot pin provided the third.
Early navaja knives featured a single locking notch and had to be unlocked by manually lifting the front of the spring. Later, craftsmen added a ring or lever to simplify releasing the lock and a series of notches that produced a ratcheting sound as the blade was opened. Like racking the action on a modern pump shotgun, this noise was sometimes used to warn or intimidate a potential adversary and led to the navaja’s onomatopoeic nickname, the carraca.
Early Italian and French Parallels
After the Spanish development of the lock-blade navaja, Italy and France followed parallel paths. They also developed their own distinctive styles of folding knives with blade locks based on fixed back springs. French knives used a wide, external backspring that resembled a palm leaf. These “palm knives” typically used the same style of tang notch as the navaja, but only a single “tooth.” The front portion of the backspring was bent upward and drilled with a hole to accept a metal ring, which made lifting the backspring to release the lock much easier.Instead of a notch in the tang, early Italian folding knives used an integral pin that was filed into the blade as it was crafted. This pin could be round or square, but functioned the same way. When the knife’s blade was opened, the front edge of the backspring stopped its rotation. At that point, a matching hole in the forward portion of the backspring aligned with the tang pin and snapped down over it to lock the blade. To release the lock and close the blade, the front of the backspring had to be manually lifted to clear the tang pin. To facilitate this, the forward portion of the backspring was typically flared or included “ears” to provide a solid purchase. Although Italian knifemakers later added rings and levers to make the lock release easier, the original “picklock” style of manually released lock remained in use on Italian switchblades until the mid-20th century, when a pivoting front bolster release became the standard.
The Notched Blade and Backspring Lug
The next step in the evolution of the back lock streamlined the existing mechanism. Although the backspring was still fixed at the butt end of the handle, the flared “hood” at the forward end was replaced with a simple squared “lug” that extended from its lower surface. The rear portion of the blade tang featured a matching notch. When the blade was opened, the front surface of the backspring would stop the opening arc and its spring tension would drive the lug down into the tang notch. The front and back surfaces of the lug, in concert with the pivot pin, created the triangular geometry necessary to lock the blade.This style of lock was slimmer than the locks with the flared “hood,” but had to be fitted with a ring or lever to facilitate lock release. It also provided a somewhat smoother, safer action than previous designs. In the closed position, the tension of the backspring caused the bottom surface of the lug to contact the bottom of the blade tang. This flat-to-flat contact helped ensure that the blade would stay closed when not in use. Many earlier designs relied on friction or, in switchblades, the retention of the firing button, to keep the blade closed.
The “Rocker” Lock
Although the addition of rings and levers made the operation of early back-lock progenitors easier, they were still somewhat cumbersome and required two hands. To simplify both the operation and the construction of these knives, the next innovation was to create a pivoting lock bar driven by a separate leaf spring. This design also used the more refined “lug-and-notch” lock interface, but the lug was integral to a separate lock bar that pivoted at the center like a seesaw. The rear end of the lock bar was supported by a flat or round leaf spring that was anchored to a backspacer in the butt end of the handle. The spring’s upward pressure on the rear of the lock bar created a constant downward pressure on the front, lug end. When the knife’s blade was opened, this pressure would drive the lug into the notch to lock it. However, when the time came to close the knife, the user simply pushed down on the rear of the lock bar to raise the front end. This made operation of the lock release much more convenient and defined the basic form of the back lock mechanism still in use today. It also inspired one of the alternate names for this mechanism, the “rocker lock.”By the mid 1800’s the back lock was in common use by knifemakers throughout Europe. The lengths of the lock bar varied from roughly half the handle’s length to its full length, as did the style of the release. In some cases, often called “humpback” knives, the rear portion of the lock bar stood proud above the handle for easy access. Others set the standard for the more modern style in which the handle includes a scalloped recess and the lock bar is flush with the profile of the handle.
Twentieth Century Evolution
In 1964, Buck Knives® introduced one of the most iconic folding knives ever created: the Buck Model 110 Folding Hunter®. This legendary knife and its smaller companion, the model 112 Ranger®, set a strong standard for folding knife form in the 1960’s and 1970’s. Many other companies emulated these designs—including their full-length back lock mechanisms. Although the longer lock bar provided enhanced leverage, it made one-handed closing of the knife more challenging.In the late 1960’s, aspiring knifemakers Harvey McBurnette, Dick Dorough, and W.T. Fuller worked together at a tire factory Alabama. After Fuller tragically lost one of his hands in an industrial accident, the three men collaborated to design a folding knife for Fuller that could be easily operated with one hand. Their approach was to take the full-length back lock that dominated the market, shorten it, and adjust the spring tension to ensure reliable lock engagement. This allowed the lock to be easily released using only one hand and created the modern “front lock” or “mid back lock” folder. Although this design certainly had historical precedent, it was distinctly different than the market trend at that time.
In 1977, Al Mar left his position at Gerber Legendary Blades to found his own company, Al Mar® Knives. Mar, a former U.S. Army Special Forces soldier with a Master’s Degree in Industrial Design, was heavily inspired by the custom makers of the time—including Harvey McBurnette. Mar appreciated the advantages of the front lock design that McBurnette favored and decided to incorporate it into his tactically oriented line of folding knives. Ever the gentleman, Mar graciously credited McBurnette for the inspiration.
A few years later, Al Mar introduced Spyderco co-founder Sal Glesser to his production partners in Japan. In addition to serving as a key element of Spyderco’s establishment as a knife manufacturer, Mar also gave his blessing for Sal to incorporate the mid back lock into his designs. In 1981, the Spyderco Worker™ model revolutionized modern folding knife design. Its pocket clip offered convenient, top-of-the-pocket carry, while its Trademark Round Hole™ allowed swift, positive, one-handed opening with either hand. Combined with the ease of one-handed closing afforded by the mid back lock mechanism, these features set a new standard in the efficiency, speed, and reliability of folding knife operation.
Today, the back lock still offers many significant advantages, including strength, reliability, ease of use, and completely ambidextrous operation. These qualities are further accentuated by modern manufacturing methods, which ensure ultra-precise tolerances and fitment of the mating parts. Although its has evolved to incorporate subtle refinements like the Boye Dent—a scallop in the rear of the lock bar to help prevent unintentional lock release—its basic form has remained substantially unchanged. The result of a long and fascinating evolutionary process, the back lock is here to stay.