The radius of hollow is very important to skaters because it determines how the blades feel on the ice. It’s set during sharpening. When you get your skates sharpened, you can request a particular radius of hollow. What if you don’t know what hollow your blades have? Or if you want to check that the hollow on your blades is what you want it to be?
To answer these questions, use a blade gauge. Blade gauges aren’t readily available commercially, though experienced skate technicians generally have one (or a set, depending on the design). I made my own out of aluminum using the CNC router at CIADC.
To use them, try to fit the arm of the gauge into the hollow on the bottom of the skate blade. Here’s an example.
9/16″ is what I asked for last time I got these skates sharpened. The person who sharpened them did a great job!