The GA5021C angle grinders have been developed as the most advanced models of the Makita GA5010 series. The electronic control system provides constant speed control, soft start, current limiter, anti-restart protection and an LED power light. The Super Joint System (SJS) reduces vibration and helps to ensure greater user safety and longer tool lifetime, while the large trigger provides ergonomic control. Makitas Super Joint System was introduced to help prevent damage to the tool and protect the user from injury. SJS is a mechanical clutch system that features a coil spring wrapped around the internal drive spindle. The coil tightens around the spindle when the machine is started, to deliver the motors power smoothly and efficiently to the drive shaft or spindle. If the blade jams in the material being cut, it can potentially overload the motor, but Makitas SJS instantly disengages the drive to the disc and the drive spindle rotates freely, before engaging again to reduce the risk