I used to have notes from a discussion I had with Harland Sharp about them and can't find them. But, I remember getting off the phone with them feeling they weren't too confident about them. But my opinion, I'm not a fan of the aluminum rocker body with the considerable amount of offset the rockers have from roller to pushrod. They are spring limited to what they can handle because of it. T & D's use a steel body. After running my T & D's this year, they've been flawless. Consistent lash. Plenty of oil to the springs, cups and rollers. They Can handle a double valve spring without issue.