Hi; I responded to this problem from Mr. Harwood. I assumed that the epoxy was dried and that it was applied to a standard shaft butt extension, which is ribbed. Hence my solution to the problem. Scrape it off of toss the plug.
However, if the epoxy isn't set and its still in a semi-liquid state, the simplest way to wipe it off is to, well, wipe it off. Use a rag. If that doesn't work, dip the rag in lacquer thinner and wipe the plug. If that doesn't work, throw the plug away and start over. What's a plug cost, a buck? TFlan
