This mirror is mounted within a mount for 20mm and 25mm mirror sizes. The mirror has high reflectivity and is gold plated for this reason. The 20mm mirror is referred to as 20mm because this is the diameter of the mirror. The mirror has two sides. The back has a silver finish, and the front has a gold finish. The gold side is gold-plated to maximize the laser reflectivity. We have these in both 20mm and 25mm sizes. The 20mm thickness is about 3mm. Cleaning: To effectively clean the mirror, use some alcohol and a Q-tip. Spray some alcohol onto the Q-tip and gently rub the gold side of the mirror. Then use a lens cleaner or similar fabric to dry it. Mounting: Unscrew the mount inside the mirror holder. Then unscrew the nut that holds the mirror in place. Then place the mirror into the mount. You will see the lip inside. Place the mirror silver side up. When it is securely fastened, just secure the mirror back into the mount.
