Full JIT relies on a number of underlying and supporting processes. king of which is suppliers making items of that are "Quality Assured", so that product can go straight to line. With such parts there should be no need for spares to be made available as part of the production supplies. However as I have previously stated, we manufactured parts that we assured, but that did not stop the poor handling process and operator errors at the caravan manufacturers damaging appliances as they handled them.