I guess what they didwas by far the easiest way to do it (so that's what they did!), but if lamps and lamp holders were to be invented today, I imagine that it would not be regarded as acceptable for the supply to be connected to to the 'male' contacts - since that certainly would not be acceptable for any other sort of connector/connection situation.Does a BA22d have female contacts and does it receive a plug?
Kind Regards, John