Bleed and Purge valves used to vent to atmosphere and to assist in calibration. They are available in 316 stainless steel only.
Vent plug Male NPT Pipe Thread

For a complete ordering number, add the desired size designator 8N (1/2" NPT ) or 4N (1/4" NPT) e.g. VPM - 4N/S316 Vent plug Male 1/4" NPT