Working my way round my new (to me) bungalow I am checking light switches and wall sockets. They have all been fitted with 30mm screws (did they used to be called bolts?) which makes them difficult to refit. I am going to get some 40mm screws but I'd like a 3.5mm tap with handle to ensure the threads in the sockets are OK. The bungalow as built in 1983, might the sockets have imperial threads from then? Some of them are right pigs to screw in.
Many thanks.