Rolled threads are much stronger than cut threads, just as a forging is stronger than a casting, and for the same reasons. As the metal is reshaped under heat and pressure the grain follows the new contour.

I don't know of any glow plugs that are not rolled threads, glow heads are different. They are usually cut threads.

Regarding an error to the point of 33 tpi, it's not going to happen whether rolled or cut.

Bill.