Loctite

242 Threadlocker, Blue, 50 ml

$13.20

Blue on the optic screws. Medium strength, so the dot stays put through a season and still comes off with a hand driver.

The blue one, and blue is the whole point. Loctite 242 is an anaerobic medium-strength threadlocker — it cures in the absence of air once the screw is seated, resists the vibration that walks a mount loose, and still lets the fastener come out later with ordinary hand tools. That is what you want on a red dot or a mount; the red threadlockers hold harder but expect heat to get them apart again, which is not a thing to be doing to an optic. Henkel rates it for metal threads up to M36 and a service range of −65 to 300°F, with a set time around ten minutes on steel and full cure overnight. Apply it above 50°F, on clean dry threads, one drop is plenty. Use it with a torque driver rather than instead of one — the Wera on this shelf is the other half of the job. This is the 50 ml bottle, part 23398.