Yes, the Standard rides on the treadle belt and does not use an O ring. Most of my treadles are like this, and then the bobbin winder pushes (or pulls) to come in contact with the belt. you can tell by where the "wheel" lines up - most line up with the treadle belt and not a hard surface. I do have a few that the bobbin winder lines up with the flywheel and those use an O ring.