A V-belt is a friction drive, so the whole purchase decision rests on dimensional discipline rather than a headline power rating. This guide sets out how a v-belt manufacturer should be judged: whether it can state the section, the datum length, the compound and the length tolerance for every belt it ships, and then prove those numbers with records. It walks through classical A, B, C and D sections, narrow SPZ, SPA, SPB and SPC profiles, the 3V, 5V and 8V family, wrapped versus raw-edge and cogged construction, and the Li, La, Ld and Lw length designations that cause most selection errors. It then covers compound grades for antistatic, oil, heat and cold duty, a four-step selection method for a real drive, the failure modes we see most often, and the procurement questions that matter: minimum order, lead time, price drivers, matched sets, OEM marking and packing.