A 6x28 stud base plate designed especially for wagon beds or large locomotives. The plate is equivalent to two plates thick at the edges but only one plate thick where all the holes are. It has various holes, 6 each end along the centre line that fit a #5302 Bogie Plate (or the #5300 motor unit). There is another similar hole exactly in the middle but I'm not sure what it's useful for. There are two more 1x2 holes near the middle that are just right for feeding wires through since the 2x2 plates of the #5306 or #5311 just fit. This allows you to take power from the motor unit and feed power to headlights which is how it works in the locomotive of #4558.