ITR4A15 5599 NGK iridium premium spark plug.
For 6 & 8 cylinder Mercruiser inboard engines. Also fits many automotive applications.
Thread diameter 14mm
Thread pitch 1.25mm
Seat type: tapered
Reach: 17.5mm (.689mm)
Hex size: 5/8" (16mm)
Terminal type: solid
Gap: .059" (1.5mm)
Resistor: yes
Priced each.
M6