I have found in Bunnings something that works,it's the two way screw.
Called J & J bottle screw 4MM (in stainless steel).
You can cut with angle grinder the size you need,smooth down with file.
Internal diameter is just right size for king screw external diameter is just a fly's wisker larger, but goes in not to tight.
And you have enough to make more.
Works for me.
On speaking to a gunsmith at Military shoot for Remembrance Day Australia, you need to make the length to fit according to number of king screw turns etc.
He said the directions are on this site have not found it yet.
Hope this helps.
Just found it........
look up "Stock fitting Torque" Peter Laidleron this site.