Caps & Plugs makes press-fit end caps and insert plugs for round, square, and rectangular tube — chair legs, fence posts, railings, 2020 extrusion, or any hole that needs filling. The key decision is the type: a plug goes inside the tube (enter the opening's inner size), a cap fits over it (enter the tube's outer size). Crush ribs are what make the fit forgiving — they squash a little on insertion, so a measurement that is off by a few tenths still grips. If a test part runs loose or tight, nudge Fit Adjust rather than remeasuring. Everything prints support-free as oriented. PETG or PLA both work; for outdoor furniture feet, PETG handles weather and load better.