There are several different types - from hexagon socket flange head screw plugs with or without O rings (in steel or stainless steel) or with oils seals; hexagon socket head parallel screw plugs in standard, perforated, shouldered, or short versions; to socket head cap screw plugs (in steel or stainless steel) with or without precoat seals.
"Hexagon socket flange head screw plugs are particularly useful in high-pressure hydraulic systems capable of impact pressure to 49Mpa", reports Amanda Laughton. "They are, therefore, most appropriate for high pressurised hydraulic machines, compacted, and safety-enhanced applications."
