Nylon glides are the standard glide if no glide is specified. They work well on all types of surfaces.
Metal glides are for use on carpeted surfaces only
Felt glides are for use on vinyl or ceramic surfaces and eliminate the vibration noise that occurs when using regular glides. Do not use on carpeted surfaces. Felt does wear out quicker then nylon so the glides do need to be replaced more often.
FRONT CASTER OPTION
Casters are available for most wood frame chairs (see seating pages for exact models they are available on.) The casters are installed on the two front legs and regular glides are used on the back legs. Chair is still stable when someone is sitting in it but is a lot easier to move when there is no weight on the legs.