Box of six Marklin 24230.

A box of six makes a half curve, 180 degrees.

C Track Curved Track, Radius R2 = 437.5 mm / 17-1/4 inches
Every piece is 30°.
These are the standard length pieces for a R2 radius curve.

Charlie's Tip: If you need 1/2 the length, use a 24215.
If you need a tighter circle, or circle inside this one, use the R1: Marklin 24130 pieces.
For a circle outside this one, use R3: Marklin 24330!

Read Charlie's blog on C-track curves