The first fundamental aspects of a brake caliper, such as its shape and the materials for the pads, depend on ... the discs. Therefore, it is necessary to briefly mention this component of the system, although a more in-depth and detailed analysis will be the subject of a future article. Mainly, brake discs can be made of cast iron or martensitic stainless steel series "AISI 400" (AISI 410, AISI 420, etc.), which lends itself to being enriched with carbon and heat treated, i.e. hardened to give it greater hardness (over 50 HRC). Usually, cast iron is suited to pads made of organic material (so-called "lining", black in colour, so to speak); steel is suited to pads made of sintered material (with a mixture of copper, iron, etc., the "recipes" for which are jealously guarded by "sinterers"). Other differences between the two materials are the specific weight (7.3 Kg/dm3 for the cast iron, almost 8 Kg/dm3 for the steel); and the fact that steel, unlike cast iron, does not rust, with the possible exception of a light patina that is "self-removing".
Other materials may include ceramics and carbon, but their use is more complex (and in some cases prohibited) and, for this reason, please see the future article that has already been mentioned.