Both are still copper plugs. I see no differences in these specs. I guess I'll just get the 438's. Still would like to know why...
438
14mm Thread Size, 19mm (3/4") Reach, 5/8" (16mm) Hex Size, Gasket Seat, Resistor, .290" Projected Core Nose, Copper Core, Heat Range 12
VS
412
14mm...