Mark, at the time that your 551A was manufactured, it was intended to be used with a separate 101A wall-mounted ring generator. The 118A came out much later and a bracket was designed to use it in the 551B and C versions. These brackets had completely different designs. Both were made of "unobtanium" then and certainly are now. Cable ties to secure it to the interrupter were generally the normal installation procedure.

Jeff: Mark's KSU is the 'A' version that had a Hubbell Twistlok Midget connection between the power cord from the power supply and the appropriate extension selected for the installation. As you can imagine, it became very costly to maintain these custom cords, so with the 'B' version, it came with a standard NEMA 5-15 cord connection. The piggy-back cord on the ring generator was designed to simply fit in-line with the original power supply connection.

Ed Vaughn, MBSWWYPBX