The Yale Door Closer 3501 is constructed of a cast aluminum alloy. It is considered a Grade 1 Closer, which is the highest grade possible. The closer features an adjustable spring tension, and separate closing, latching and back check intensity valves. The full plastic cover is standard on this closer. This door closer replaces the older 3501BF closers. The new version is Barrier Free Complaint. The hole spacing is 3/4" x 12", the cylinder is sometimes cast 20-3301-1001 on the back of the cast aluminum cylinder. This closer ships with all of the mounting hardware and parallel arm bracket.
Inside the plastic cover you might find these numbers on a sticker, 3501/3501BF and 8501/8501BF. This is because the Yale and the Norton are the same closer, but with different name plates on them.