Okay!
 

Found the OFNA board and they say one washer on the glow plug with no idle bar. What in the wild world of sports is an idle bar?

I've never seen a plug with the bar either. I think if you were to get one by accident it would look different enough that you would scratch your head and think, gee I probably should get a different plug. :p But I'm sure somebody else will answer your question better. Did you try searching glow plugs at tower hobbies site? You'd probably be able to find a pic there.

back in the early days of nitro, some glow plugs had a bar that ran across the glow plug and covered the coil. Idle bars were used because some motors stalled when at idle, these bars would help prevent the motor from stalling by having the bar cover the coil from cold fuel when at idle. Motors today don't need them because the bar will make contact with the piston, and most motors can idle for long periods of time before stalling.

This is a pic of an old plug with an idle bar.