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A set containing 64 R120 curves to form a full circle.
Large R120 radius of the curve, dedicated to large custom train sets. These curves are one size bigger than R104. These curves allows for very high speeds without derailments. 
Detailed explanation of R120 radius
The R120 is the radius measured from the center of the circle to the centerline
between the rails using the LEGO® stud as the unit. LEGO® stud is 8mm. The space needed to have the full R120 circle can be calculated as follows: (120 + 4) * 2 * 8mm = 1984mm = 1.98m. This measures the diameter (2 * radius) of the outer shape of the track - that's why we added 4 studs in the formula.
In general, the formula for calculating the outer diameter of the track circle is:
(R + 4) * 2 * 8mm
Dedicated ballast plate: Ballast Plate R120 Set - 8 pieces for 8 R120 tracks