@Ben.Friberg: Because different size diameters put more or less torque pressure on the file. The toughest situation is a short radius curvature on a narrow canals. Wide canals can be instrumented with less torque, which is why we can do step back rather than crown down in those canals. Where canals are narrow you may decide to sacrifice efficiency for safety. This is why you make a file selection based on the specific requirements of the canal you’re dealing with. In the EndoSequence Blend Protocol I’ve accounted for these requirements and that’s why this protocol is universally robust. Cheers.