connection between axle and carriage
輹 refers to a specific structural part of a carriage: the connection or coupling between the axle and the carriage body. It is a technical term for that mechanical linkage.
輹 combines 車 (vehicle, carriage) with 复, which likely contributes the sound フク and may relate to the idea of returning or repeating, possibly referring to the cyclical stress on the axle connection.
The left side is a carriage 車, and the right side 复 looks like a complex joint. Picture the axle fitting into the carriage body through a sturdy, interlocking connection.
For フク, imagine the axle connection being secured with a strong hook: hook -> フク, and the hook keeps the carriage firmly attached to the axle.