The spring that fits between the lens housing and the diode in the module will work as it is smaller in diameter than the 9 mm lens housing. The slotted side is never used as that is the side that goes toward the focus ring. There are two types of springs I have seen. The old one is longer, but has less tension and a newer version that is shorter, but has a lot more tension than the older version. I don't like the new version and never use it. I always use the longer spring with less tension. Now, when I use an acrylic lens the housing is too short to screw all the way into a focus ring. So, I used fingernail polish to attach it to the focus ring and only allow the ring to grab the first thread. This is because you can remove all of the polish with acetone if you make a mistake and need to do it over. But, I never use a spring with an acrylic lens because the tension will break loose the polish, but it still works fine as I normally have to tweak the focus anyway, because it moves when I remove the lens cap.
