...What do the terms grille and register mean?
A grille is a vent that does NOT have a damper. A register on the other hand is a vent that does have a damper.
......What is a supply grille/register?
A grille/register is a vent in which the air is coming out of the wall, ceiling, or floor -- supplies air to the space.
......What is a return grille/register?
A grille/register is a vent which takes air from the space back to the fan or air handler.
......What is the difference between wall and floor grilles/registers?
Floor grilles/registers can support the weight of a person (extra bracing) while wall ones cannot.
......What is a list grille size?
The list size is typically the opening (hole) size. This is the size entered into the ordering page. The actual grille size
will be undercut (see grille specifications for details) to allow the grille to slide into the opening.
......Can I paint a 'mill finish' grille?
Yes, but it is not easy. Mill finish grilles might still have surface oils from the manufacturing process. You would
have to degrease and prime the grille before painting. Dayus recommends the silver painted grilles if you inted to paint
a custom color. The silver will act as a primer layer for your paint. ......What is a damper?
A damper is a device on a register that regulates the airflow. 
