This is Roofing  knife. It comes with four  blades in the handle and one in the knife. The handle hinges opposite the blade end and holds the extra blades.

✦ Adjustable Blade Depth

✦ Over length: 7" 

✦ Heavy Gauge Zinc Plated Steel Construction

✦ Includes 5 Extra Blades in Handle

✦ Roofer Bowtie Knife