I know of some builders totally happy with 87106 swabs. I was until I had a wheel melt on it and saw it had a bit wider base and I had not sized it in a dummy wheel first, but then I thought- how difficult am I making the polishing with a surface not really parallel to the bore? I switched over to the 87104 cylinder, and yes, you still might need to shape it for some bores, but at least the entire surface is polishing at the same time and in my opinion, the bores look better quality.