Dial Y-For yo-yo (Points for where the reference comes from). The Fast 401SD is the latest successor to the 401 series of yo-yos with a twist controlled recess. A H-shaped body with the 401 adjustment system. Just turn the dial and you will set the recess to the level of responsiveness that you want. Precise aluminum body, gives this yo-yo a precision feel with the added ability of adjustable response.