I bought this type of banana plug from Ebay (see images below). However, I can't figure out how to insert the plastic insulation
The insulation is not threaded. It seems you just jam the metal part inside. However, the wide part of the metal does not fit into the hole. It is about 5.5mm whereas the hole in the plastic insulation is about 4.75mm. The plastic is also semi-hard so pushing does not make it stretch to size.
Should I drill out the hole to make it larger? Are you supposed to heat the metal part up and push it into the plastic holder when hot so that it melts to fit?