That is indeed a take-apart spark plug. Always use the larger hexagon for removing and installing it. If necessary you can restrain it by the larger hexagon and unscrew the smaller hexagon. You can then clean the entire insulator with a fine wire brush. Don't take it apart repeatedly though - the gasket that seals the insulator to the steel outside part is not intended for re-use. All spark plugs used to be made that way, and I was one of those who were disappointed when manufacturers found that they could roll a raised up part of the outside steel part inward to hold the insulator in, thus saving money (and also overcoming one of the more common leakage paths for spark plugs that had suffered from amateur maintenance). Incidentally I think you'll find it can be removed with a standard A/F socket or ring spanner, but if it happens to have an 18 mm thread rather than the modern 14 mm thread, it might be a larger size than the 13/16" A/F that was usual from the 1950s onward. The only really odd spark plug spanner I can recall was required for the Model T Ford and vehicles of that ilk, which had 7/8" Gas threads instead of 18 or 14 mm.
I suggest you do not operate that edger without both fitting a proper blade, and installing a side cover. It looks quite dangerous to me. I agree it looks professionally made, but like Victa's built in edger, it was a very bad idea.
