Use this knife guard to cut your bagel, not your fingers. This simplistic design was inspired after my girlfriend and I both cut our fingers trying to slice through three day old bagels. Fits Bagels that are up to 5" in diameter and 1.75" thick. Use a long, serrated knife for best results. Will leave small portion of bagel uncut at the bottom. Hold edges and push down on top of cutter for best results. I recommend glueing some rubber padding to the bottom of the knife guard to get grip to countertop surfaces. 

I'm able to customize these to add lettering, symbols, shapes, etc... The last image shows an example of the knife guard I'm printing off for my girlfriend and I. This model has been updated to thin out the walls and reduce the amount of material required after printing the initial model.