“Type M (BS 546) Plugs
They are distinguished from Type D plugs by their larger pins and current rating of 15A. The central earthing pin is 28.89 mm long and 8.71 mm in diameter, while the hot and neutral pins are both 18.94 mm long, 7.06 mm in diameter, and spaced 25.4 mm apart.”
“Type M (BS 546) Plugs They are distinguished from Type D plugs by their larger pins and current rating of 15A. The central earthing pin is 28.89 mm long and 8.71 mm in diameter, while the hot and neutral pins are both 18.94 mm long, 7.06 mm in diameter, and spaced 25.4 mm apart.”
This is the first result I got from a quick Google search. Today we learned, friend.