Electric male plugs with rounds have slotted pins

[jackson6612]

I have observed many big electric male plugs (that come with refrigerators etc.) with rounds have slotted pins. What purpose do those slots serve. I wish I had a camera with me so I could show you one. Please let me know.

 

[Studiot]

The pins need to make good contact in the socket.

With flat pin terminations a spring can easily be made to press against the flat when inserted, making a good connection.

This cannot readily be done with a round pin, whcih relies on a tight fit for a good connection.
Moreover after many insertions the socket tends to slacken.

So (some) round pin designs have a slot that can be spread a little to retighten the fit and re-establish good contact.