Solid Brass Surfboard Vents with O ring. Brass vents are drilled and ported so they are not just "a screw in an insert nut" Pressure relief does not require knurled screw to be completely removed.  Open slightly and internal pressure is equalized even while out in the lineup. 
NOTE: Knurled screw really likes to put a hole in your wetsuit when you go over the falls so best to set this vent into a recessed pit. See pic.