These cut outs allow Lucas K2F magnetos, as fitted to BSAs, to be stopped by earthing the points through a wire rather than pressing in the button on the end of the cover. This method allows the magneto to be cut out and the engine stopped without leaning down to the magneto. Also by attaching a wire they become compatible with ignition keys, lanyards and oil taps, they also offer a range of security and safety benefits. 
 
These caps are often sold to be used in conjunction with our oil taps.