In 1979 AYK released their very first RC car, the RX1200 but also their famous and very expensive GX1200 diff as option part for this car. At this time most 1/12 cars were using either a solid rear axle or a open gear type differential using molded plastic gears. Ayk went with a unique design with their diff, looking like a scaled down version of a 1/8 diff like AMPS or PB but using two crown gears and two bevel gears. The diff case is machined from aluminium with the spur gear connected by a hexagonal hub. Driveshafts are made from 5mm steel with the crown gears attached inside the diff case. The rear wheels were using just a grub screw for fixing to the driveshafts, no wheel hub needed as with most other cars.
The GX1200 diff was sold as complete conversion kit with larger bearings, thrust bearings and new rear axle blocks matching the larger bearings. Exactly the same diff was used later with the RX2000 and some versions of the RX3000. The NX101 car made for R&D Ishihara used this type of diff again but this time an improved version with stronger diff case.
At the picture you can see an early version of the GX1200 crown gear diff with black diff cover (aluminium). Another version with silver diff cover was used for the RX3000 and newer conversion kits. The improved NX101 diff later was using a black fibreglass diff cover. Differences could be found also with the spur gears, all of the diffs came with spur gears of 63, 65 and 67 teeth metric size but the early spurs were made of a dark grey plastic, the RX2000 spurs of white nylon and the NX101 spurs of light grey plastic.