Adaptor fittings enable a connection from a pipe, hose or cable to another pipe, hose or cable which is a different size or type. They can be used to reduce the flow or even terminate the pipe, hose or cable run. For example you may have a manifold that has imperial female threads and you need to fit a pipe that has a metric male end. An adaptor will connect the two together.
Currie & warner manufacture medium to large volume adaptors used in the electrical connector industry. Many old installations have imperial threads and most new fittings are metric. Thus requiring adaptors to bridge the gap.
If there is a requirement to reduce the flow of liquid in a piping system, Adaptors can be used to restrict the flow at a constant rate.