Loctite 243 Threadlocker is a general-purpose, medium-strength blue anaerobic adhesive specifically engineered for locking and sealing metal threaded fasteners between 1/4" to 3/4" (6 mm to 20 mm) in size. It fills the gaps between tightly fitting threads and cures completely in the absence of air to protect assemblies against severe shock, vibration, fluid leaks, and rust. Unlike older formulas, it offers a major advantage: it is highly oil-tolerant, meaning it effectively cures even through minor surface contamination from motor oils, cutting fluids, or anti-corrosion treatments without requiring aggressive cleaning.