Here is my take on “retooling” the Outemu Sky switches (forgive me if this is the wrong term, it was the term I was taught for this procedure). There are other switches that can benefit from this treatment as well.
First, the problem. The center hole on Outemu Sky housings can be a tight fit for some stems. What’s worse, the hole has some rings / ridges around the inside that you sometimes feel the switch stem rub against, making it feel rough / gritty / chunky / etc.
Hopefully in this pic you can see the rings better. They are way down in there, but the stem reaches them. The tip of the stem can rub across those like a washboard. Doesn’t feel great.
Here is the hole after modification. The process is thus: Get about a 2.34-2.35mm drill bit (or reamer). Push or walk the drill bit or reamer down until it bottoms out at the bottom of the hole. Then run the drill at full speed for a few seconds. Some people prefer to then remove the drill slowly from the hole while the drill is still running. I prefer to stop the drill before pulling it out, because it seemed like pulling it out while it was running was leaving spiral scratches around the inside of the hole. You can probably see in this picture, no rings, looks smooth. Be sure to clean any shavings or dust out of this hole when you’re done.
Here are tools you can use. On the left is a 2.35mm drill bit, and on the right a 2.34mm reamer bit, which is the tool I prefer for this job.
Here is the drill bit I tried:
Here is the reamer I tried, which does an even better and creates smoother walls inside of the center hole: