LTWFITTING 3/8 in. Brass Compression Cap Fitting (10-Pack) HF61CAP610 - The Home Depot
LTWFITTING 3/8-Inch Brass Compression Cap Stop Valve Cap,Brass Compression Fitting(Pack of 60) - Household Rough Plumbing Valves - Amazon.com
3/8 in. O.D. Compression Cap - Danco
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
3/8" Brass Compression Cap, Lead Free - RJ Supply House
Sioux Chief® 3/8" Compression Brass Cap at Menards®
Brass, For 3/8 in Tube OD, Cap - 4CXY9|6BLP6-B - Grainger