it works seperately from the outside thumb stud, basically a index finger pulled back against the pad and it helps to open the blade outwards. harder you pull faster it pops open type of thing. it fits in the frame and contacts the blade itself. It can also be swapped into and out of the frames if you have several craters and want to swap parts.The lock itself is a liner lock and its lock up is quite audible and positively locks the blade.