Individual letters and numbers can be classified by their thickness or dimension.
Dimensional letters are used for all types of signs, interior and exterior. They can be lighted or not illuminated. Dimensional means they have some thickness and look three dimensional when they are installed on the wall. Small dimensional letters are used for directional signs or business signs outdoors. Thickness vary from 1/8″ to 5 or 6″ like the channel letter signs that hold lighted parts inside of the letter.
Lobby or reception logo signs are better looking signs when are made with dimensional letters. The more dimension, the more attractive is the sign.
Flat letters and numbers are cut out from materials which thickness varies from .040″ up to 1/2″, their thickness is due to a solid piece of material. Flat letters can be installed to the wall by leaving a 1/2″ space in between the letter and the wall. This type of installation combined with the appropriate lighting can make the letter look three dimensional due to the shadow that the letter throws to the wall.