The nail of the plug is in a mountain shape, and it will not catch on routing and removal. Because it will not touch, nails are also hard to break and it is saved.
Also, at the time of production, it is useful without troublesome handling of boots.
Although it is very nice to break the claws, it is very good, but a little expensive is a bottleneck, but it is easy to end up and also has special caulking tools, so continue using it. I wonder if it will be a little cheaper?