The D300XX series has a striated finish, and is designed to be used with the 1250 series vertical mail boxes. The D400XX series has a smooth finish, and is designed to be used with the 1400 and 1500 series horizontal mail boxes.
Alphabetical directories are required by the USPS, when there are 15 or more mail receiving tenants in a building.
All models are 0.75"D (20mm) off of finished wall surface
NOTE: 'x' indicates the color of the directory unit