The Ninja 600R was the name given to the Kawasaki ZX600 line of motorcycles sold in North America. It also went by GPz600R and GPX600R in other countries. It was built from 1985 to 1997 with minor improvements throughout its production.
The name ZX600 has a letter and number that follow. The letter denotes the major changes, the number after the letter denotes the model year. The North American changes are: ZX600a 1985-87, ZX600b 1987 (very rare with aluminum frame) sold as the Ninja 600RX in North America, ZX600c 1988-97. The ZX600a and ZX600b are very similar with the exception of the ZX600b's aluminum frame. The ZX600c did not get the aluminum frame but did get new body parts, stiffer rear suspension and a new head. The head changed from bucket tappets to rocker arms. It also shed 25 kg (55 lb) bringing it down to 180 kg (400 lb) compared to the ZX600a.