What feature of a loose-pin butt hinge allows for easy removal of a door?

The feature of a loose-pin butt hinge that allows for the easy removal of a door is that the pin can be removed. A loose-pin butt hinge is designed with a pin that is not permanently fixed in place; it can be easily pulled out, allowing the two hinge leaves to separate. This design is particularly useful when maintenance or replacement of the door is necessary, as it allows for quick and efficient removal without the need for special tools or complicated procedures.

In contrast, a fixed hinge would not have this removable feature, which would prevent the door from being easily taken off. An adjustable hinge refers to a type of hinge that can be fine-tuned for alignment but does not inherently allow for door removal. Concealed hinges are designed to hide their mechanisms, making them aesthetically pleasing while complicating the removal process. Thus, the removable pin is the key feature that distinguishes loose-pin butt hinges and facilitates easy door removal.