The walls of lightweight aluminum rims are too thin to support concentrated from spoke nipples directly. Steel eyelets are crimped into the spoke holes of aluminum rims to reinforce them and to prevent nipples from galling the rim when they are tightened. Good hollow cross section rims have steel sockets, held in place by crimped eyelets that distribute spoke loads to both the inner and outer bed of the rim. This method of spoke support permits thinner walls and lighter rims. Rims without sockets to distribute loads to both walls often crack around their spoke holes with use.
Steel washers can be used instead of sockets, but these are uncommon because even thick ones are relatively low in bending strength compared to a deep socket. Therefore, washers must be nearly as heavy as sockets to carry the same load. Since only one wall of the rim supports the washers, this wall must be thick enough to give the same strength as a thin wall of a socketed rim. Rims that use washers are only lighter than rims with sockets when weighed without their washers.