Bit Breaker Adapter Plates are located in the Master Bushin g drive pin holes and provide a 13-9/16” square to accommodate Bit Breaker. They are used for MPCH, MSPC, MDSP and MSP. P/N 1816 used for 23”~49-1/2” master bushing. P/N 1815 used for 17-1/2”~21” master bushing.