The wrist band of a watch decides whether I can easily put the watch on, and, take it off, and if it is comfortable to wear. For wearing comfort, I find it relevant that the band end does not slip out of the band loop.

Here is a rubber band by NOXIN/NIXON (depending on what direction you read the text on the band parts) that has a rectangular cut-out in the band loop to allow the band end with a rectangular protrusion to fit in.

Here is a photo of the rectangular cut out of the band loop.

Here is the rectangular protrusion that is meant to go inside the cut-out.

Here is a photo that shows both the rectangular cut out at the top of the image, whereas the band loop has a hole.

The bottom of the image shows the rectangular protrusion mounted on the band end. When the watch is worn, the band end has to fit its rectangular protrusion into the rectangular cut out of the loop. That then efficiently prevents the band end from slipping out. The watch is a cheap China branded Invicta.

To allow me to single-handedly slide the rectangular protrusion underneath the loop, I used a few tools (file, Dremel) to take off one side of the edge of the rectangular protrusion. As a result, I can more easily slide the band end underneath the loop and still have it stay there.

In the image below you can see the bottom facing long edge of the rectangular protrusion that has been filed off at an angle. Not it slides in (but not out) of the cut-out quite easily.