20577: Curve 1/30 grad
(6 pieces = 180 grad)
20571: Curve 1/60 grad
(3 pieces = 180 grad)
20572: Curve 2/30 grad
(6 pieces = 180 grad,
for 4-lane extension)
20573: Curve 3/30 grad
(6 pieces = 180 grad,
for 6-lane extension)
20578: Curve 4/15 grad
(12 pieces = 180 grad,
for 8-lane extension)