The back lock (or mid lock or front lock) is a lock which loks the blade by using a notch in the blade (numbered 28 on the pictures) and a springloaded lever to go into the notch (numbered 25 on the pictures) . By pushing on the lever in the handle (As indicated by the shadowtraced part of the drawing in picture 2, numbered 18), the lever is free from the notch in the blade and the blade can be closed. During the closing the spring loaded lever still applies force to the blade and thus make it easier to close in a controlled manner, even one-handed. The positioning of the lock on the knife usually dictates wether it's a front lock, a mid lock or a back lock, but the terms are used interchangeably, and thus, we call it a Back lock, whereas what Spyderco uses is actually a positive front lock. The front lock is hardly new. The Boker knife company of Germany was using a front lock in about 1903, but its origin may be a century or more previous. Its use was popularised in the current generation by the late custom maker Harvey McBurnette, but the concept was never patented. McBurnette introduced the front lock to Oregon designer Al Mar, who began using it on his knives in the 1970s. Sal obtained permission from Mar to use the lock design and to include it in his patent application, then under the name the Mar/McBurnette front lock.