Twin blade knives have a pair of thumb buttons and hold two blades at the ready. This one is a FatMax Xtreme. Bostitch makes one too.
Here it is with the standard blade out.
Here it is with the Accutrax Pencil Blade extended. It looks like you could cut with it, but in fact, the knife is now set up for use as a very fine marking pencil.

You’ve probably seen Stanley and Bostitch twin blade utility knives. Instead of a single thumb piece for extending and retracting the blade, they have two thumb pieces, each controlling a separate blade. Contractors typically load these knives with one standard blade and one hooked blade (as would be used to cut asphalt shingle or linoleum). That way, they can carry one knife instead of two.

Ken Abrahamson, a contractor in Sussex, Wisconsin, recently came up with a better setup for his twin blade knife. He told me this in an email message: “Just now as I was building a table for a cement siding guillotine, I had a moment of clarity. For real tight marking I have started using Accutrax graphite blades in a small utility knife. My right hand pouch always has those small things I use all the time, but I realized I was carrying too much. I have a FatMax Extreme 2-bladed utility knife. Well you should be able to see the punch line from here…”

Abrahamson took one of the steel blades out of his twin blade knife and replaced it with an Accutrax Pencil Knife. Now, if he has his knife he also has a fine marking pencil. It’s a clever idea and I wish I had thought of it myself.

In case you’re not familiar with the Accutrax, it’s a blade-shaped piece of reinforced graphite (pencil lead material) that fits in a utility knife. Run it across any surface that can be marked with a pencil and it will leave a razor-sharp line. There is an excellent demonstration of it in the video below—starting at about the 1:05 mark.

If there are any tool related tips you would like to share, please contact me at It will help greatly if you can send photos.

The Accutrax Pencil Blade shows up at about the 1:05 mark.