PORTHOLES EXTERIOR DOOR - amazing windows fitted to outside doors. For security reasons use carriage bolts on the exterior side of these portholes for them not to be unscrewed. For adequate insulation on exterior doors, the portholes are fitted with insulation glass. Additionally, the glass used in these portholes possesses strong burglar-proofing qualities. Mounting the porthole to an appropriate door thickness is achieved by fitting the matching insulation glass.