Nitrile rubber covered oil seals for temperatures up to 110c.

R21/SC (SC usually marked on the seal for single lip) and R23 or TC (TC also marked on the seal for a twin lip) R23 Oil seals have an extra wiper (dust lip or twin lip). These seals have rubber Nitrile OD with metal insert, primary lip and an additional dirt/dust lip (sometimes called a wiper) moulded with the overall seal width. They can also be referred to as "Semi dual" lip type, as the name suggests they help prevent the ingress of dust/dirt into the primary lip area.