This document establishes the specifications relative to family C (gears) for lubricants, industrial oils and related products of class L (see ISO 6743-6). This document deals only with lubricants for enclosed gear systems. Lubricants for open gears and greases for gears (enclosed or open) are covered by the other parts of the ISO 12925 series (i.e. ISO 12925-2 and ISO 12925-3). This document is intended to be read in conjunction with ISO 6743-6. The following categories specified in ISO 6743-6 are covered by this document: CKB, CKC, CKD, CKE, CKSMP, CKTG, CKES, CKPG, CKPR, CSPG, CSPR, CTPG and CTPR. Detailed information about the different types of gear, and lubricants, and their selection for gearbox design and service conditions can be found in ISO/TR 18792.