These pulleys are made of galvanized steel, and are designed for use on overhead sectional garage doors with extension springs. They can be used either as stationary pulleys on the door frame, or as the pulleys attached to extension spring. Garage door hardware can be replaced yourself if you're comfortable with DIY projects, but some users might find it difficult. Before buying, make sure you're comfortable replacing or installing these pulleys yourself. Check the detailed instructions, or watch our How-To videos for replacing garage door hardware.