What does it matter? No one can see them back there anyway.
And before you comment about me half assing everything (because I see it coming), I've done it both ways (with correct plugs).
you tell me how one of those (in the correct thread- 5/8-11) is ANY different than the "correct plugs". if you hold them side by side, they're NOT different except for the rediculous price tag the "correct plugs" carry.