Only running one fuel tap? Need to block off your other fuel bung? These 1/4" Brass fuel plugs are perfect for the job. They are brass so they won't bugger the thread on the tank either.

-1/4" NPT thread
-Brass construction
-3/4" Overall length
-7/16" Thread length

Please note: These are a little tight when threading in. Presumably this is to prevent fuel leaks.