When selecting a grinding wheel for the inner angle of circular saw blades, it is recommended to choose one with a narrower diamond flat surface. 

During grinding, the diamond abrasive surface can fully sweep across the inner angle of the saw teeth. 

Specifically, the inner end of the contact area between the diamond and the saw tooth will move off the flat surface and into the inner bevel, resulting in sharp, smooth and straight saw teeth, 

As shown in the picture.

In contrast, if you use a grinding wheel with an overly wide abrasive face, the innermost contact point cannot fully clear the saw tooth surface during operation. 

This leads to incomplete grinding and uneven saw tooth surfaces, as shown in the reference image.