Everbilt 3/8 in. Comp Compression Brass Cap 801039 - The Home Depot
C74-002LF - Jones Stephens C74-002LF - (61C-6) 3/8" OD Brass Compression Cap (Lead Free)
Brass Compression Cap 3/8"
3/8" Brass Compression Cap Stop Valve Cap Brass Compression Cap Male Threaded for Water Pump Ports, Drain Pipes, Oil Sensor Holes, Engine Block Holes (2 Pieces) - Amazon.com