Aeroquip series 2082 (Ref. SAE 140109E) External Pipe/Plug.  Also available in stainless steel as part number 259-2082.
Items
2082 Pipe Plug Adapter

2082 External Pipe/Plug

2082 Pipe Plug Adapter

2082 External Pipe/Plug

2082 Pipe Plug Adapter

2082 External Pipe/Plug

2082 Pipe Plug Adapter

2082 External Pipe/Plug

2082 Pipe Plug Adapter

2082 External Pipe/Plug
Thread P1 N/A 1/8-27 N/A 1/4-18 N/A 3/8-18 N/A 1/2-14 N/A 3/4-14