A snap-off knife (also called a utility knife, Stanley knife or box cutter) is a hand tool with a retractable, segmented blade where snapping off a dull section reveals a fresh, sharp cutting edge. It is one of the most commonly used tools on building sites and in workshops.
How does a snap-off knife work?
The blade of a snap-off knife has pre-scored segments (usually 7 or 8 per blade). When the tip becomes dull, you snap off the front segment using pliers or the built-in snap-off cap. The next segment then forms a new sharp point.
Snap-off knives come in two standard widths:
- 9 mm — for fine work such as wallpapering and marking
- 18 mm — for heavier work such as insulation, roofing felt and plasterboard
Application
The snap-off knife is used on site for:
- Insulation material — cutting mineral wool, EPS and XPS to size
- Plasterboard — scoring and snapping plasterboard sheets
- Roofing — cutting bitumen felt and EPDM membranes
- Sealant and tape — removing old sealant, cutting tape
- Marking — scoring lines on timber or sheet materials
- Wallpapering — trimming wallpaper to fit
Safety tips
- Always cut away from your body
- Use a straight guide for straight cuts
- Snap off dull segments immediately — a blunt blade requires more force and slips more easily
Related terms
- Tools
- Insulation
- Plasterboard
- Roofing
- EPDM
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