[Bob Kontak]

Gaps set at above the 0.040" - like at 50-60 thousandths - will give the juice a good reason to find a better ground point. That means that if your wires are tired the large gap may cause arcing between wires or to a metal ground (e.g., air conditioning support bracket) or into your hand because it is easier for the voltage to land there rather than jumping the electrode gap.