Where a floor simply ends
The obvious case is a doorway onto carpet, where the new floor is higher than what is beyond it. The less obvious ones are a sliding door track, a hearth, the edge of a raised area, and the point where a floor stops at an external door.
All of them have the same shape of problem: the floor finishes, the edge is exposed, and there is nothing at the same height to join it to. That is what separates this profile from a T molding, which assumes there is.
What an end cap protects
The cut edge of a floor at a doorway takes a great deal of wear, because everybody walks over it and because it is the edge things get dragged across.
An end cap covers that edge with a profile designed to take the traffic, and it does it while leaving the expansion gap underneath open. The second job is the one that gets overlooked, since a covered gap looks the same as no gap at all.
Square nose, and the names
This shape is sold under several names, square nose among them, and the profiles vary between makers. The related one to know is a reducer, which ramps down to a lower floor instead of finishing squarely, and the two are sometimes listed together.
What stays constant is the condition it answers. Describing the edge, a floor finishing higher than what is beyond it, is a more reliable way to find the right piece than searching by name.
Which way round it sits
An end cap has a high side and a low side, and it only works one way round: the high side sits on the floor and the low side faces whatever is beyond.
That sounds obvious until a doorway has floor on both sides at different heights, where the question becomes which room the profile belongs to. The higher floor is the one that takes it.
End cap against a threshold
Where a floor stops at an external door, the end cap has to sit against a threshold or a track that was already there and was not designed with it in mind. Height under a door and space in front of a track are both limited, so that junction is worth looking at closely.
It is worth looking at before the floor is ordered instead of after, since the height available under a door and the space in front of a track are what decide whether a profile fits. The flooring trim page covers the rest of the range.
