With this small part, rails of any length can be made. Two of these parts and two brass or aluminium rods with 3 mm diameter are required.
Example: For a rail over 4 fields, two metal rods with a length of 228 mm are required (5 fields 288 mm).
Since the printer cannot print an accurate 3 mm hole, the holes may need to be re-drilled with a 3 mm drill.