Nap Length VS Surface
1/4", 3/16": Fits for smooth surfaces like metal doors and plaster.
3/8", 1/2": Fits for smooth and semi-smooth surfaces like drywall.
3/4": Fits for semi-rough surfaces like wood or a textured ceiling.
1", 1-1/4": Fits for rough surfaces like stucco or a heavily textured ceiling.
1-1/2": Fits for extremely rough surfaces like concrete blocks.