Originally Posted by Kiljosh
Yea clean it with a tap, if that doesn't work try retapping it with the next size up.
I've actually done this, and used a 1/4-20 when I converted
Kirk's intake to a post-deleted upper. If that hole is so bad that
1/4" will not work, go 5/16" and that will work for sure. Those
taps and bolts are cheap too, lots less than metrics.