I know that tubes are identified by the inside diameter. My 1 1/4 galvanized pipe has an inside diameter of 1 1/4 and an outside diameter of 1.66. These plugs are marked with the outside diameter. Prescott 1 1/4 plugs will not fit 1 1/4 zinc plated or black tubing. In an ideal world, the description for a 1 1/4 pipe plug would be "Plug for 1 1/4 to 1 7/16 ID pipe". Outer diameter 1.50 inch. "I had hoped so. After it snaps into place, you'll need to use a screwdriver to pry off the cover. Significantly cheaper than a threaded steel toe cap. And a nice cap if you don't have pipe threads. The plastic seemed durable.