A removable particle collector for an apparatus which separates metal particles from lubricating oil. A valve assembly has a bore that provides a passage into the reservoir from outside. A valve element is normally biased against a valve seat to close the bore. A plug has a stem which when inserted into the valve assembly bore forces the valve element away from the valve seat. A portion of the stem is magnetized to attract ferromagnetic particles in the reservoir. A plurality of balls rotatably project from a surface on either the valve assembly or the plug and are received in a plurality of locking grooves in the other of the valve assembly and the plug to secure those components together. The balls are lubricated by fluid from the reservoir and can rotate to reduce wear which could loosen the components.