This MechMan Marine certified high output 170 amp 6 phase alternator is a great upgrade for boats using the popular 6.61 inch center-to-center bolt pattern alternator. This style alternator was used by many boat manufacturers from the late 1960's through 2018. (check the technical drawing against the measurements of your stock alternator to see if this unit will fit your application) This alternator comes with a simple single wire pigtail plug included. Simply connect an ignition switched 12V+wire from the original alternator plug to the supplied alternator plug for proper function. This unit features (12) diodes and twin rectifier plates for excellent durability with high-end audio installations. The included 6 groove serpentine pulley measures 2 inches. This unit meets or exceeds SAEJ1171, ISO 8846, and USCG Title 33 standards for ignition protection.