Kyosho 87051-03 is a 45 Degree Corner Expansion Kit for the MINI-Z Grand Prix Circuit 50. It allows users to expand their existing race circuit by adding 45-degree corners. The kit includes 12 pieces, which can be used to create a variety of different layouts. The mats have a smooth surface on one side and a rougher surface on the other. The rough surface produces better grip, so users can choose which surface to use depending on their preferences. The kit also includes circuit barriers, which can be used to prevent cars from leaving the racetrack.