Example is shown is in door style C. Hand painted in Bone by Farrow & Ball
This is a slide in Mantel for a false chimney.
Each side is 320mm - 400mm wide.
Also make sure that you check your hob manual (or website) to get the minimum height from hob to extractor. As a guide it is likely to be about 650mm for an electric hob or 760mm for a gas hob, but you MUST install according to your hob manufacturers instructions!