The triangular blades come with two straight edges and one angled, serrated edges. The two straight edges work equally well front and back. The serrated edge only work as intended, like a chisel.

In fairness, there is one valid reason why the company would have chosen to make it impossible to reverse the blade: to avoid support calls and warranty claims from people trying to use the serrated edge the wrong way around.

Because if you think about it, they went out of their way to make the socket one-way: it would actually be cheaper to manufacture the notch on both sides than the way they made it on one side only. So they really did intend to ensure the blade can only be mounted one way.

But here's the thing: you have to be really, REALLY dumb to use the serrated edge in reverse and not realize it. It's completely obvious that the tool isn't working right, and there's something sharp sticking up instead of down on the glass. So I don't buy the idiot-proof anti-warranty-claims argument: I'm totally certain it is done to limit the life of the blades.

Although mind you, it's rather academic: when an edge is spent, I simply sharpen it with a fine belt on the belt sander and it's good for another few months anyway 🙂 But of course, you need a belt sander if you want to do that.