518 general purpose, primerless, semi-flexible, form-in-place anaerobic flange sealant. It cures – even in the presence of minor surface contaminants – to seal close fitting joints between rigid metal flanges, and will flex with minor flange movements. It provides resistance to low pressures immediately after assembly of flanges, and is ideal for use on aluminum substrates where you need very good flexibility. Typically used as a form-in-place gasket for pumps, thermostats, compressors, transmission housings and axle covers, it not only works on active metals (e.g. mild steel) but also on passive substrates, such as aluminum with a low copper content. You can expect gap performance to 0.01" (0.25mm).