20th century lock-blade pocketknives were popularized and marketed on a wider scale. Companies such as Buck Knives, Camillus, Case, and Gerber, created a wide range of products with locks of various types. The most popular form, the lockback knife, was popularized by Buck Knives in the 1960s, so much that the eponymous term "buck knife" was used to refer to lockback knives that were not manufactured by Buck. The lockback's blade locking mechanism is a refinement of the slipjoint design; both use a strong backspring located along the back of the knife handle. However, the lockback design incorporates a hook or lug on the backspring, which snaps into a corresponding notch on the blade's heel when the blade is fully opened, locking the blade into position. Closing the blade requires the user to apply pressure to the spring-loaded bar located towards the rear of the knife handle to disengage the hook from the notch and thus release the blade. The Walker Linerlock, invented by knifemaker Michael Walker, and the framelock came to prominence in the 1980s. In both designs the liner inside the knife is spring-loaded to engage the rear of the blade when open and thus hold it in place. In the case of the framelock, the liner is the handle, itself. The Swiss Army knife product range has adopted dual linerlocks on their 111 mm models. Some models feature additional "positive" locks, which essentially ensure that the blade cannot close accidentally. CRKT has patented an "Auto-LAWKS" device, which features a second sliding switch on the hilt. It can operate as any linerlock knife if so desired, but if the user slides the second control up after opening, it places a wedge between the linerlock and the frame, preventing the lock from disengaging until the second device is disabled. Tactical folding knife Buck's original lockback knife was originally marketed as a "folding hunting knife" and while it became popular with sportsmen, it saw use with military personnel as it could perform a variety of tasks. Custom knife makers began making similar knives, in particular was knifemaker Bob Terzuola. Terzuola is credited with coining the phrase "Tactical Folder". In the early 1990s, tactical folding knives became popular in the U.S.A. The trend began with custom knifemakers such as Bob Terzuola, Michael Walker, Allen Elishewitz, Mel Pardue, Ernest Emerson, Ken Onion, Chris Reeve, Rick Hinderer, Warren Thomas, and Warren Osbourne. These