I believe the bipod by Harris is a #9.

R.W. Hart also makes an adaptor that you cannot even see once the bipod is installed. It is a pc of alum that is flat on the stock side and rounded on the bipod side, and it has a hole in the middle for your bipod stud to go thru. The only thing I had to do on mine was to get a longer stud, and I also put a strip of non-slip padding between the stock and adaptor so it wouldnt scratch my stock. I paid $9 for mine right from Hart, but I thought that Sinclair, Brownells, or Midway was selling them as well.

I'll see if I can find the link to it.