SuperStreets D21 Curve (1) D16 Curves nest inside D21 Curves for realistic 2 way traffic. SKU: 6-21281 Dimensions: 8 D21 Roadways to a 21" diameter circle Gauge: Traditional O Gauge price: 3.49 year: 2007 rail line: None Minimum Radius: None Catalog Year: 2010 Catalog Title: Lionel Signature Edition Volume One 2010 Road Number: None None D16 Curves nest inside D21 Curves for realistic 2-way traffic. Manuals Find the latest manuals in our support section. Replacement Parts Buy any replacement parts in our support section. Contact Contact a service station to fix your product