Treadmill safety key: Magnetic work, can work easy and quick on most treadmills requiring a round treadmill safety key. Part Number: SFP-T02-SK,Replacement for Sunny Health & Fitness Treadmill Models: SF-T7643, SF-T7705, SF-T7705 Smart, SF-T7705B, TM100 Design purpose: Our safety keys solve your fitness equipment needs to keep you and your treadmills or elliptical moving at a fraction of the cost or major repairs. Easy to use: Easily clips to virtually all types of clothing so you can forget about the key while you walk or run. One year warranty ! please contact seller if there is any problem . Replacement for Sunny Health & Fitness Treadmill Models: SF-T7643, SF-T7705, SF-T7705 Smart, SF-T7705B, TM100