Covers are made from a removable adhesive vinyl which has been 'domed' to give it a 3D look, not just a one-dimensional sticker.
All Switch Covers are for PDL600 series brand switches (that is the number one brand in NZ); and are for a single switch or a double switch (single switch is one hole double switch is two holes).
A single switch + Dimmer = a double switch
Single switches are the same regardless of whether they are a light switch, your Sky TV jack, your Telecom jack or whatever.
To recognise a PDL switch you can either pull the existing cover off and see what is written on the inside of the cover or on the bit left on the wall, or measure the size of the hole where the switch is, if it's a 24mm square hole it's a PDL.