Bill, they should be used with curved base followers with a radius of 0.75". Made my own followers years ago by getting someone to weld some Stellite on to standard followers and then using a pair of turned discs each side of the follower to act as a guide I hand ground them. Ah the optimism of youth, but it worked. 140 mph at the end of a half mile sprint on a bike ridden to the meeting. They just would not work with flat followers.