Try Metric........ A lot of times a 12 point wrench works better.
For a Road King they are: M8 X 1.25 with a depth of: 1.28 in., (32.54) mm
Yours should be the same as mine 1/4-28 and you need a 5/16 wrench or socket to remove it.
Uh oh. Guess I'll pull one and take it to the store with me. Hoping to save a trip. Thanks for the responses.