Ian, so do those plugs have a different hexagon size (I am not familiar with K series)? My "normal" 14mm plug socket is 13/16" about 21mm hex. I can't measure my 10mm plug socket because that is in the garage and I am not going out there tonight but looking up 10mm plugs says the hex is 5/8", approx 16mm which would explain the Halfords description I have just edited this to correct an error and add info