This is a four pack of blister carded curve track pieces for use with the UNITRACK N gauge track system The Curve radius and degree descriptions describe what portion of a complete circle (360) is made from each section and how big that circle will be (in this case approximately 17", or double the radius Radius measurements for curves such as these are measured from the center point of a circle to the center line of the track, making it easy to keep track of how large your layout will be when you're still in the planning stages!