BELMONT ALLOYS 2451 and 2491 are bismuth-base, eutectic, low-melting alloys that are used for tooling and production aids; 2451 melts at 117 F and 2491 at 136 F. They provide the engineer with easily castable material that is ready for use as soon as it freezes. The alloys can be recovered easily and recycled into new uses any number of times. Their major use is for lens blocking when grinding glass and plastic lenses and optical components. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on heat treating and machining. Filing Code: Bi-3. Producer or source: Belmont Metals Inc..