This Gymnastics I-Beam Clamp fits 4” to 9” I-Beams. This means the bottom flange or bottom plate of the I-Beam is 4" to 9" wide. I-Beams are shaped like the capital letter "I" when viewing from the end. Will fit some open web steel joist. I-Beam clamps can be used to attach ceiling hung rings, climbing ropes and spotting rigs to I-Beams.