Front box?

no cable entry on front of a bell box.i take its an old system so you will have to replace the rusty bell box with a plastic one there are lots out there but you must be carefull falling off a ladder is no fun,call an engineer out ,its safer and he will advise you on what box to fit,its just not a case of removing the cover,when u do that you will create a tamper that you may not b able to reset

gts
February 2016

Is the hole an un-used cable entry? You should be able to source a plug easily enough. Measure the diameter of the hole and do a search for "Blind Grommet" "blind gland" on ebay or similar.

You dcould even fit a normal cable gland with a short length of plastic in place of cable

Is the hole threaded? Something like this may suit: https://www.tlc-direct.co.uk/Products/EK20BP.html

Anon
February 2016