In working with angle metal, I have need to place an end cap on either end of a piece.

This thing takes the base form, and fills in the end, to make a convenient end cap. By default it is sized for 1/8" X 3/4" angle metal. Using the OpenScad, you can change many of the sizing parameters.

The fitting is comfortable, meaning it goes on easy and comes off easy. If you want a tighter fit, you might want to make the extents, or the thickness slightly smaller. That, or just put a dab of hot glue in the slot before you slip the metal inside.

1) Print a couple
2) Slip onto the ends of angle metal
3) Rejoice

This fixture is actually practical for usage as it gives you a cap to the end of a piece of metal.