These plugs do the job but are not very the level of durability thickness for my outdoor horse stalls.

TheFatRancher only reviews items he has actually used!I was very excited to find these tubing caps that were sized to true 4x4. However, installation is problematic.The retaining flanges are exactly the same size as the cap, continuous, and thicker than necessary. the result is that they don't fold down readily, and when they do the thickness stacks. that is, there isn't enough space between flanges for the flange before it to fold against the inner wall. Thus, there is too much material to fit in the steel tube I was attempting to cap.The manufacturer needs to do one or more of the following: A) Make the flanges into tabs (non-continuous) so that the user has a better chance of fitting them into the tube; B) Make the flanges shorter; C) Make the flange thinner so it is more malleable.A user could try trimming some of the flange material. Though this may be a knucklebuster. I tried heating the cap up prior to installation. This did make the plastic softer, but deformed the cap. Moreover, there was still too much material to fit between the inner cup and the tubing. So it wouldn't fit.So, great idea, and the size is right. But the design needs some tweaking.

These 4" square tubing plugs fit nicely into my aluminum tubing to give me finished ends. These caps are as described and fit actual 4" X 4" square tubing. They give a nice professional look to the tubing and protect both the tubing and the floor from damage. I would recommend this product.