To replace your old letterbox you need to first establish which of the three sizes it may be: 12" Standard (or Scotia), 12" Slimline or the 10" Standard (just measure the overall height and width). Then just lift up the outer flap and measure across the postal slot (Height x Width). This will allow you to check the size of the inner sleeve that fits through the slot in the door. Once you know this information then check the details of the relevant letterbox. In some cases there may be some minor modification needed of the hole in the door but the letter boxes we show are the best sizes available to fit all known letterboxes. These letterboxes are all covered by mechanical guarantee and made/designed in the UK.