internal O-ring grooves?

[Cooper]

I had been using tools that I ground myself for a while. Would never get consistency and forget about taking a couple more thousands off after original cut. Finally purchased these and still look new. First time I used the purchased ones I thought they came loose because I couldn’t feel anything. But it was cutting like butter. (In brass). Used them on stainless and on low carbon steels. Still like new. Unless you have a good understanding of cutting geometry and a pretty precise grinding wheel I (knowing what I know now) would spend the $20-40 on it. But on the flip side forming your own tools is rewarding once you get it correct. Me personally, not that I don’t want to learn and understand cutting geometries, I would rather learn how to make the parts . And if you are making grooves for the cylinders try to get the shortest shank tool. More rigid=better cuts. With these ones above I can secure them in quick change tool holders. A dedicated holder would be nice but these have flats ground into them so as long as they are on centerline and parallel I’m good to go. Hope this helps .