With the opening restrictor (ZOZ 010KC), an easy-to-fit safety catch, you can regulate the extent to which your VELUX roof window opens. compatible with GGL / GGU centre pivot windows only. Please note that this opening restrictor cannot be used on VELUX top-hung roof windows Box was delivered open from Velux but has never been used, I purchased two from velux but only needed one in the end.
eBay