Ok I've wound a few coils now and it is getting easier and easier as I gain the ability. I have ordered some different gauges of magnet wire just experimenting. The last one I wound will give a decent spark at 4 Volts a weaker spark at 3 volts. Runs my Atkinson engine really good and makes it a good starter just barely flip it over top dead and shes off and running. The one I just finished is about the size of a c size battery. Was going to use the shell of a c size battery but changed my mind and am going to stay away from a metal casing and using pcv instead. I'm thinking of using a couple of them on my Mini Hog engine.