Retaining compound is used when press or slip fitting cylindrical components that are not threaded. It fills the gaps between parts, creating a rock solid connection. 609 formula is an all purpose, quick curing compound that is perfect for general press fit applications for gaps up to .005" that will not be exposed to excessive heat. 620 is a high heat slip fit formula that will withstand temperatures of up to 450 F and fill gaps up to .015" while sealing the metal and preventing corrosion. 638 is a super heavy duty compound for use in high stress applications, for slip fit applications of up to .010".