Needed a new bespoke loft Hatch rather than try and patch up the existing non standard size unit. Having carefully checked and double checked the opening dimensions and deducted the recommended 5mm from each I ordered a standard white insulated unit with extra wide 50mm bezel. Unit arrived very well packed and fitted like a glove, and the extra width bezel covered up any old damage/decoration to the opennings edge. The only comment I would make is that installation would be easier if the hinge mechanism was of a design such that you could remove the loft hatch door from the frame, and thus offer up and fix the frame on its own.