Top Pick Loctite® 243 Primerless, Oil Tolerant Removable Medium Strength Blue Threadlocker is designed for the locking and sealing of threaded fasteners between 1/4" and 3/4" (6 to 20 mm). It not only works on active metals (e.g. brass, copper) but also on passive substrates such as stainless steel and plated surfaces. It tolerates minor surface contaminations from various oils, such as cutting, lubrication, anti-corrosion and protection fluids.