Abstract: A fluid filter has a fluid inlet, a fluid outlet, and a filter element in the fluid pathway, and is provided with a by-pass which includes a fluid pressure indicator. The by-pass comprises a cylinder attached to a cover and removable therewith. The cylinder has one aperture which provides fluid communication between the cylinder and the inlet and has another aperture which, when open, provides fluid communication between the cylinder and the outlet and hence provides a fluid pathway between the inlet and outlet which by-passes the filter element. A piston is movable within the cylinder responsively to fluid pressure from a first position where it closes the second aperture to a second position where the second aperture is open. The cylinder can be removed and mounted in a first position which provides both an indicating and a by-pass function or it can be rotated to a second position which provides only an indicating function.