For composite and UPVC doors, From the Anvil recommend using their door letterbox which is supplied as a full kit and contains a tunnel and brushes to reduce drafts and insulate the door. The sleeve inside the letterbox also protects the door from moisture and masks the aperture cutting.

From The Anvil - 46554

• • Overall Size: 315 x 92mm
  • Opening size: 249 x 41mm
  • Fixing centres: 283mm
  • Maximum door thickness: 72mm
  • Minimum doo thickness: 42mm
  • Satin Marine SS finish

  Supplied with matching SS bolt through fixings.