Utility knife: setting it up and changing the bit or blade

Learn to set up a utility knife, extend the blade safely, and change or snap off a blunt one.

UK-01Learn the parts before you touch the bladeA utility knife (also called a Stanley knife or box cutter) has a plastic or metal body, a slider on top that pushes the blade in and out, and a lock that holds the blade at your chosen length. Inside the body is a channel that holds spare blades. Find the slider and the lock before you extend anything, so you know how to retract the blade quickly if you need to.

UK-02Open the body and load your first bladeMost utility knives open by sliding a button on the side or undoing a small screw at the back. Open it flat and you'll see a slot near the front where the blade sits, plus a storage channel behind it for spares. Slide a blade into the front slot with the sharp edge facing away from where your hand will grip, then close and lock the body shut.

1 pack of 10 · Snap-off utility blades

Buy:ScrewfixB&QToolstationAmazon

UK-03Set the blade length for the jobPush the slider forward until only 5-10mm of blade shows for card and thin plastic, or a bit more for thicker material like carpet underlay. The beginner mistake is extending too much blade - it flexes, wanders off line, and is far more dangerous if it slips. Only expose as much blade as you need to cut through the material in front of you.

UK-04Cut with the material, not towards yourselfAlways cut away from your body, never towards it, and keep your free hand well clear of the blade's path. Use a steel rule or straight edge as a guide rather than your fingers. Let the blade do the work with light, even pressure - forcing it is what causes it to skip sideways and cause a cut.

UK-05Snap off a blunt segmentA snap-off blade is scored into small segments so you can break off the blunt tip once it stops cutting cleanly. Retract the blade fully first, then use the snapping tool built into most knife bodies (a slot with a metal edge) to snap the end segment off cleanly. Never try to snap it with pliers or by hand held near your fingers - the broken piece is very sharp and can fly off.

UK-06Change to a fresh bladeWhen snapping segments no longer gives you a sharp edge, or the whole blade is used up, retract it fully, open the body, and slide the old blade out from the front slot. Take a new one from the storage channel or a fresh pack, and load it the same way as before, sharp edge away from your grip. Dispose of old blades wrapped in card or in a proper sharps container - never loose in a bin bag.

1 pack of 10 · Snap-off utility blades

Buy:ScrewfixB&QToolstationAmazon

UK-07Check you've set it up rightA properly loaded knife has a blade that sits flat and doesn't wobble side to side when you press it gently with your thumb on the flat, not the edge. The lock should hold the slider firmly at whatever length you chose - it shouldn't creep forward or retract on its own. If the blade wobbles or the slider won't lock, open it up and reseat the blade before you use it.

Some links may earn us a small commission at no extra cost to you.

Save this as a project

Back to all guides