Either the manufacturing tolerances or QC of the two packs that I received was subpar. About 40% of the top housings did not have enough clearance for MM P3 stems to smoothly travel through the housing, causing the linear stems to exhibit a tactile bump during actuation. This could also be a problem in conjunction with the stem manufacturing, but while troubleshooting, I found changing the top housing solved the problem faster than changing the stem. For example, a narrower housing might fit 1 in 10 stems well but a wider housing fit all 10 of the same stems. Overall love the idea of the MM product line as it made frankenswitching easier and cheaper but found the quality hit or miss. Would suggest any buyers to purchase an excess in case you find a failure rate similar to mine.