This will fit a variety of engines, including f-heads and l-heads (based on the instructions).
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“NOS New SURE START Engine HEAD BOLT HEATER 110V Willys Jeep Hurricane GMC Case
NOTES/Particulars/Please read all:* This is a Vintage NOS (New Old Stock) Sure Start HEADBOLT HEATER. These were quite popular back in the day for older engines, for ease of start in cold weather. Your grandpa knew what he was doing, and these heaters work quite well when installed correctly. THIS HEAD BOLT HEATER IS FOR VINTAGE ENGINES USING 7/16-14 Head bolts. That is the head bolt shank is 7/16″ (.437”) in diameter X 14 THREADS PER INCH ONLY. ENGINE APPLICATION IS ON PHOTO #3. ALSO the instructions show what headbolt location to use with your engine.