LGB
R1 30 Degree Radius Curved Track

Walthers Part # 426-11000, p. 76 Walthers 2003 Big Trains Reference
G scale, $8.99, currently in stock at Walthers
This product is on-sale today for $7.98

 
This basic R1 radius curve of 30 degrees means 12 sections make a 360 degree circle.