Both our 10" and 12" letterplates have a robust ABS moulded frame set with internal and externally sprung flaps. The external flap having been designed to be opened to approx 147°, giving a generous and clear access to the sleeve apperture for the posting of mail.
The method of springing the flaps, torsion bars, having successfully achieved a 40,000 cycle endurance test opening to 140°. This would equate to four times a day use over a 27 year period.
A secondary internal nylon brush seal has been introduced to reduce air filtration when in use. The standard ABS sleeve set is 40/40 and would cover door thickness 38 to 78mm.