Our family had a combination kit. Sold to adapt a hot water bottle to enema/douche use. The kit contained a stopper with nipple that would be screwed into the neck of the hot water bottle and the provided rubber hose slid over the nipple. The other end of the hose had a threaded fitting for attaching one of the four included nozzles.
The smallest was a child enema nozzle. Straight sided, slightly narrower than a pencil and about 2.5 inches long.
The next was an adult enema nozzle. It was about 6 inches long with the profile of a baseball bat and about the width of a pencil at its widest.
Then there was the retention nozzle. It was about 5 inches long with a bulb at the tip. (It reminded me of a rosebud on a stem.) The bulbous tip was 3/4 inch in diameter at its widest with a straight shaft.
Finally was the douche nozzle, it was straight, 8 inches long with 4 fluted with holes that came out the sides of the nozzle.
After my aunt died, a new nozzle appeared in the box. I was a curved douche nozzle, same basic dimensions of the original, but curved along its length.
My first enemas (at age 10) were given with the adult nozzle with only 3 inches inserted. Gradually, more was inserted as I grew. My mom then switched me to the retention nozzle. It stayed put (mom didn't need to hold it in place as she had with the other nozzle.)
When I started giving myself enemas, I tried all the nozzles. The retention became my favorite since I liked to walk around house naked as I took and held the enema.