This is one medium-length plug that will work well even with engines .15 or smaller! The reason: no idle bar to interfere with the piston. The TOWER Power Glow Plug doesn’t need an idle bar to hold its heat. There’s no need for you to miss out on savings, either: TOWER Power Plugs are sold in sixes and twelves as well as singles. And as always, buying in multiples means more savings for you.