ORIGINAL: jedijody
The cap does fit your spark plug, it's just very hard to get on and off the first few times. You have to push very hard, if you don't wear a glove it will likely hurt your hand and leave a mark.
You were exactly right.It took a bit of doing and a pair of leather work gloves but it finally snapped on there. Ran the engine for the first time today and all I can say is "Wow." I am impressed to say the least. I am running it on an older Goldberg Sukhoi at 12 lbs. and it really flies it great.