I have bought for my Func KB-460 with MX Blue switches to the noise by the so-called "bottoming-out" to dampen these O-ring. Due to the lighting, I decided for the "clear" version. The material appears to be similar to silicone and dampens the stop perfectly. When attaching the rings, it is helpful to use the cover of a Filsstiftes (The fit of the thin Stabilostiften very well) to put the rings evenly as possible and quickly to the keys and to save yourself a Gefriemel and Gefummele :) The typing feel remains almost unchanged, but the stop is a little softer, which I find positive.