Stanley produces a retractable work knife called the FatMax 778 that allows the user to lock the blade in place to produce straight cuts. Blades on most retractable work knives can be loaded by unscrewing the side of the knife body. Due to the FatMax 778's design, it is not possible to load blades into the knife like other conventional retractable work knives. Extreme caution should be used while handling and loading blades into the FatMax 778.
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Push the sliding button located on the top of the knife to its forward-most position.
Insert the back of the blade into the opening at the mouth of the knife. Orient the blade so the sharp edge faces down. You will notice two notches on the top of the blade, which are used to secure it.
Push the blade inward until the internal mechanism makes contact with the notches and clicks into place. You may have to wiggle the blade a little bit to aid the internal mechanism.