I am having a problem with a FS ASP nitro engine I read some where FS need a special glow plug can any one tell me what that plug is what is it's number

Four stroke engines do not need a special glow plug. An OS Max type F plug or a Fox Miracle plug will work well. Describe the problems you are having with your engine. I'm sure there are numerous folks in this forum who can help you.

OS F but the popper is correct, they will run with most any long reach plug. The four stroke plug retains it's heat longer for the second cycle. I run type Fs but in a pinch I often run the OS # 8. I also run the YS plug and the four stroke plug from Hanger 9. Then I gave the Miracle plugs a try and they work very well.
I scored a complete sheet of the OS F plugs so when I get back to flying I will treat all my engines to new plugs.

Yup. Gene is correct. Gotta be long reach and toward the higher end of the heat range. Gotta keep the fire going in these engines that only fire on every other revolution.