Utility knife blades in bulk: Stanley standard blades in 50 and 100 packs, Milwaukee 50 packs, and Milwaukee micro carbide general-purpose blades in a 100 piece dispenser. Blade profile is what to match to the knife you already carry — standard, hook and heavy-duty blades are not all interchangeable across every handle, and a hook blade is for cutting roofing and carpet toward you without diving into the substrate. Carbide-edged blades cost more and last several times as long on abrasive material like drywall and shingles; plain carbon blades are cheaper and are meant to be changed often. A dispenser with a used-blade slot is the safest way to buy these where more than one person is changing blades.
