These knobs make it is easier to turn the potentiometer with your fingers, and it makes it obvious that these are to be turned to adjust something. Without the knob, you may be using your fingertips and accidentally pushing out other components on a breadboard, or using a screwdriver and stripping the soft white plastic.

After measuring the potentiometer with calipers, I designed a variety of knobs. The easiest of all of them to use is the BladeTop. Some have a window so you can see the number on the potentiometer which indicates the total resistance. The knobs have a tight fit so you may want to stick them on the potentiometer before putting the potentiometer into a breadboard. Pushing the knobs on afterwards can be done, but sometimes the pins get bend with the amount of force needed with the tight fit. Also, if you find it is a really tight fit, the knob will not come off or you may break the potentiometer trying. Luckily these are inexpensive components.

I have a YouTube video showing the knobs here: 

I have an AnkerMake M5C and print the knobs without supports. Printing them upside down is usually better for the fit to the potentiometer. When I print them standing, the slight expansion of the first layer means I have to use a knife to clean up the edges of the underside for it to fit. If the top of the knob is not flat, e.g. the blade top, then I have to print it standing. Either way, these are very small quick prints so you can experiment.

I included the drawing of the dimensions I used for the underside if you would rather try making your own type. I plan to post a remix that is a knob with “labels” that you can print and glue in place.