There are little topcovers which fix on top of Toyota 4age engine distributors. They have alphabets written on them for identification because the fixed wire angle is little different according to design of distributor.
total there are five, 4 for sparkplugs and one for coil. The purpose is the stop wire popping out from dist. when car is running. i broke a holder while disconnecting coil from dist and had to replace it,
then found a spare dist and saw same alphabet cover on it ,