Alex's Parts Carries a line of steel pipe plugs for general automotive use.
These little gems won't be found at your local parts house or hardware store.
This size is common for blocking off NOS fitting holes in intake manifolds.
Pipe plugs always appear larger than their size suggests.
This is because the size grading is based on the inside diameter of the pipe, not the outside diameter of the thread.
A 1/16" pipe plug is intended to screw into a threaded hole which would accept a pipe with a 1/16" inside diameter.
These are popular for blocking off un-needed NOS NPT holes in intake manifolds.
Specs: