Our new speedometer plug covers up the mechanical speedometer gear access hole in the new TKO 500 and TKO 600 transmissions so they can be used on 1999 and newer Mustangs with electronic speedometer pickups. The new TKO transmissions are equipped with dual speedometer pickups, to work with either electronic or mechanical speedometer pickups. A plug is required to cover the mechanical access hole if it is not being used. The plug also fits most common Ford transmissions such as T-5 and T-45, for use on racecars without speedometers.