High quality stainless steel window hinges, friction stays. These hinges have a 17mm stack height. The Egress only option opens wider than a standard friction stay for fire escape (Note: the window must of been manufactured to anticipate an egress hinge in order to meet building regulations) The Egress Easy clean friction stay also has the option of sliding the whole sash to the centre in order to clean the window from both sides.
eBay