Perko 8503DP Medium Duty Battery Selector Switch with Alternator Field Disconnect (AFD). Polycarbonate body with brass terminals, ignition protected for use with 6 to 32 volt marine electrical systems. Continuous amperage rating 250A (360A intermittent for 5 minutes). Terminal stud size 5/16". Interrupts alternator field current on non-unitized alternators when turned OFF while engine is running. AFD: Yes. Lockable: No. Positions: 2. Includes screw terminals and surface-mount design. IP65 rated components and metal contact materials provide durable performance in boating and marine electrical applications.