O-Ring Switch Dampeners help to eliminate or reduce the noise when key switches bottom out on the downstroke.
Glorious Gaming offers thick (2.5 mm) and thin (1.5 mm) O-Rings with a choice of either 40A (soft) or 70A (hard) durometer ratings. O-Ring Switch Dampeners are suitable for most MX-style keycaps.
O-Rings can reduce the key switch's total travel. The actuation point and travel distance of a typical key switch are 2 mm and 4 mm, respectively, while some "speed" switches have an actuation point and travel distance of 1 mm and 3 mm, respectively.
The diameter of the O-Ring will restrict the travel distance accordingly, so be sure to select a size that will work with your keyboard.
You can programmatically set the actuation and release points on some highly customizable keyboards such as the SteelSeries and Wooting. This capability offers greater flexibility when choosing an O-Ring for your keyboard.
O-Rings are a relatively cheap solution to reducing the noise from your keyboard switches. Amazon also offers a wide selection of O-Rings to choose from. However, not all O-Rings are created equal. From a durability perspective, I highly recommend silicone O-rings instead of rubber. The price difference is minimal.
You may be pleasantly surprised by what a low-cost modification like O-Rings can do for you.