I think you have to have the 60mm cutter for the 60mm blades to fit. I have both a 45mm and a 60mm. Can't find the 45mm at the moment, but pulled out the 60mm Fiskars and the cutter is definitely designed for the 60mm blade. The round plastic is sized to provide support for the entire blade. I'm afraid if you used the bigger blade in a 45mm cutter, the blade would not have enough support.
Here is a link to the 60mm cutter. You can use either 45mm or 60mm blades in it:
http://www.fiskarscrafts.com/tools/t...ry-cutter.aspx
Here is a link to the 45mm cutter. It doesn't mention that you can use 60mm blades in it. Also, you can see that the entire 45mm blade is supported by plastic.
http://www.fiskarscrafts.com/tools/t...ry-cutter.aspx
I prefer using my 60mm if I am cutting with a ruler. It's easier for me. However, it's too big to use in my June Taylor "Short Cut" (flexible plastic with slots for cutting); have to use the 45mm for that kind of cutting.