I got my first real mechanical keyboard with MX blue switches, and I love typing on it... for the most part. I've been use to typing on a laptop keyboard and a
Logitech Illuminated keybaord for a long time, where they both have a lot less noise and the bottom-out distance was a lot shorter than my Filco MX blues. Although the feel of the keys was great, I still needed to find a way to reduce noise and make the keystrokes shorter. This O-ring mod killed 2 birds with one stone.
Basically putting an O-ring around the stem of the key caps reduces noise because of the rubber material, and reduces bottoming-out distance because of the thickness of the rubber. I believe the amount of noise it reduces depends on the softness of the rubber and how large the O-rings are. The hardness of rubber is measured in the Shore A scale. The bigger the Shore A number, the harder the rubber is. The smaller the number, the softer and more flexible the rubber is. Theoretically, the softer the rubber, the more it can dampen vibrations and noise from keystrokes, especially bottoming out. As for the other factor, the more material the O-ring has (basically the size), the more it can dampen shocks and noise. For O-rings in this application, the inner diameter must be 3/16" (4.76mm), or very close to that. The outer diameter can vary, and it's proportional to the thickness, which means the O-ring thickness can vary too. If the outer diameter wasn't proportional to the thickness, it would be more of a washer rather than O-ring. As for the last part, bottoming out distance is solely dependent on the O-ring thickness. A thicker O-ring will reduce key travel more than a thinner one.
Enough with the background, here is my small review. I tested two O-ring sizes shown in the picture, both were silicon 40A durometer with inner diameters of 3/16" (4.76mm). The smaller ones have an outer diameter of 5/16" (7.94mm) and thickness of 1/16" (1.59mm), while the larger ones has an outer diameter of 6/16" (9.52mm) and a thickness of 3/32" (2.38mm). Both of them does an amazing job at dampening the noise, it's hard to describe, but the best subjective description is that it "muffles" all noise associated with the bottoming-out. Under normal typing conditions, it nearly eliminates all bottom-out noise. For testing purposes, I hit the keys a lot harder than I normally type to purposely generate noise: without any O-rings, the noise was a loud "clack" when it hit the bottom, with the O-rings it was more like a a "thud". Since I had a MX blue switch, the click noise from the keys actuating was unchanged. Again, this mod only eliminates bottom-out noises. It seems like the larger fat O-rings has a higher degree of noise dampening, but not by much. And also there is a very noticeable difference in the amount of "shock" felt between no O-ring and with the O-ring mod. 40A durometer seems like the perfect sweet spot for softness. Anything harder would be less effective in dampening noise and the harsh shock, but anything softer might feel too "gummy" and not crisp enough.
The main reason why I also did this O-ring mod was to shorten the bottom out distance. I read that the O-rings currently sold only had a negligible impact on the bottom out distance. From my experience with the smaller ones, this is true. Although it did have a slight noticeable effect on bottom-out distance, for me personally this was not enough because I've been too use to typing on notebooks and thin Logitech keyboards with a short bottom out distance. I wanted to replicate this on my Filco by using larger thicker O-rings, and this did the perfect job. Although the larger ones were only 50% thicker, it made a huge difference. With the smaller O-rings, there is still enough key travel after the actuation point before the key bottoms out. With the fatter O-rings, the bottom out is nearly right after the actuation point. Both O-ring sizes did not affect the key distance for the actuation point. This reduction in bottoming out distance with the larger O-rings made the perfect keyboard I wanted: The nice feel of a mechanical switch on the old keyboards I had been so accustomed to type on. When I type, I always bottom out regardless of the key travel distance. This mod made it more comfortable and actually increased my typing speed by around 5wpm averaged over many runs on hi-game.net. I'm guessing this is because my fingers travel a few millimeters less for every keystroke and it adds up after many sentences.
I know this mod is not for everyone, I'm sure most on here has had their mechanical keyboards for years are quite use to the noise or key travel distance. But for some like myself, this upgrade made a rather big difference in comfort and feel of the keys. In the context of mechanical keyboard costs, I think for only $5-$20, this O-ring mod is definitely worth it to at least try out. Here are a few places where you can get some O-rings:
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wasdkeyboards.com: 50A (~$17shipped) or 40A (~$20shipped)
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mcmaster.com: 50A $9shipped
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kaiserreich: 50A $4shipped
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me: 40A $10shipped