i figured it out its actually pretty simple it slides out via gravity locks in place and slides back and locks in place so it doesn't slide out on its own.
all you need is a metal door or closet door slider, a cutting device (knife saw scissors whatever) the hammer off a toy cap gun, a cork or something for the hammer to pivot on, an elastic band, a ring that fits your ring finger and a length of string or band and a file. And of course a blade.

the slider should be riddled with holes place the hammer somewhere on the slider so that the end of the hammer holds the slider in place so it cant move and use a metal rod or the cork to fix the hammer in place so it can pivot to lock and unlock the blade attach the band to the hammer and around the slider so that it holds the slider in a locked position. attach the string or band to the ring and the end of the hammer and put it on your ring finger and change the length of the string so that the hammer keeps the slider locked when your hand is in a fist. use the end of the slider as a fulcrum so that when you open your hand the tension on the string uses the fulcrum to pull the hammer back and unlocks the slider. At this point in time cut the inner slider on the end where you want the blade to be adjust the blade so that it doesnt protrude when in the locked position and thats it its done all you have to do is attach it to your wrist. ill upload a tutorial drawing soon.