Hi CJ the actual square headed nipple is screwed into a hexagonal bush type that in turn has a weep hole within just buy the complete kit turn off both radiator valves and remove the outer bush with a socket/ring spanner you will get a small amount of water (if more retighten and check the rad valves for soundness) re seal male threads on the new one with PTFE replace into hole and tighten with spanner turn on valve one side only regulate water entry with new nipple when air has finished then water comes retighten the bleed nipple not to tight this time then re adjust both rad valves to suit HTH Tez