The base of the cage is just one of the components that contribute to the realisation of the filter holder. The end cap is secured with the wires welded within to protect the filter sleeve and prevent premature failure.
The end caps are produced in materials including: raw steel, pre-galvanised steel or stainless steel.

The three most-utilised types of end cap are: riveted, welded and clamped, whilst the end cap is welded for the oval cage.