Abstract: A tool for visually detecting and releasing grease overpressure from a grease nipple comprises a grease coupling in which is formed a vent opening. The grease coupling is carried by an extension tube that extends rearward towards an insert to which it is connected. The insert has a bore in which reciprocates a button bolt. The button bolt extends past a rear face of the insert to an indicator button. A piston extends through the extension tube, from the area of the vent to the button bolt. Grease entering the coupling may exit the vent and may push the piston so as to move the indicator button thus indicating potentially dangerous overpressure.