Metalwork 304 Stainless Steel Pipe Fitting, Solid Square Head Plug, 1" NPT Male (Pack of 2) - Amazon.com

Square Head solid Plug for Closing and Terminating the End of a Pipe
1" Male National Pipe Taper (NPT) threads for use with female threaded pipes
Made from stainless steel 304 for strength
Square head for increased leverage and use with a wrench
Great for blocking off intake manifold water ports, water pump ports, water temp and oil sender holes, engine block