Patent ID: 7797838

Claim:
A retractable blade knife comprising a handle having a front end; a rear end; a back surface; an open surface; a blade hole being formed through the front end of the handle; and a sliding slot being formed through the open surface of the handle; a blade being mounted movably in the handle and having a proximal end; a spine edge; a closed surface; an open surface being visible through the sliding slot of the handle; and at least one detent being formed on the spine edge of and near the proximal end of the blade and being sloping; an extending assembly being mounted between the blade and the handle and having a positioning frame being mounted in the handle beside the closed surface of the blade and having an open surface facing the closed surface of the blade; a closed surface; a rear edge; a front end; a back edge; a sliding slot being formed through the positioning frame and corresponding to the sliding slot of the handle; and a resilient rod being mounted on the back edge of the positioning frame and having a rear end selectively abutting the spine edge of the blade; and a front end selectively abutting the proximal end of the blade; a slider being mounted beside and movably relative to the closed surface of the positioning frame, being attached to the closed surface of the blade and having a rear end; a back edge; and a lock protrusion being formed on the back edge of the slider and selectively abutting the rear end of the resilient rod of the positioning frame; and a spring being connected respectively to the positioning frame and the slider and having two ends being attached respectively to the positioning frame and the slider; and an unlock assembly being mounted on the open surface of the blade near the proximal end and protruding out of the sliding slot of the handle.