Reximex RP/RPA adjustable grub screw sight

A model based on idea introduced in but using M3 heat insert and a hex grub screw. After roughly figuring out sight height, unscrew it, put it on a threadlocker and screw it back in and fine adjust. Typically threadlocker takes some time to set (and most take 24 hours to reach engineered hardness) so that should be enough.