Sk-4 safety knife with 17.5 mm trapezoidal blade with semi-automatic retraction. when the slider is released, the blade automatically retracts after cutting or when it loses contact with the material to be cut. prevents accidental injuries after cutting. powerful return spring. ergonomic handle. robust stainless steel blade channel. reversible dual-use blades. suitable for left-handed users: only reverse the direction of the blade. no tools are required to replace the blade. acid and acetone resistant. dimensions: 36 x 140 mm