Since my frame had no solid substance to attach my cork to, I need to cut a backer. I just used some particle board I had in the hoarders nest, aka garage. As you can see from this picture, I only had one C-Clamp. Hubs is pretty resourceful, he came over and locked the caulking gun on to help hold the square in place. He's my hero!
I just used my jigsaw to cut out the backer to fit in to the hole in the frame. Be sure to measure that from the backside of the frame.
So, let me give you a little scoop on the roll of cork. I looked around at some local stores for the cork I wanted and I just could not find what I needed, so I hopped on to Amazon and found what I was looking for. This stuff come in different thicknesses, so think about what you would like. The thicker you can go the better, so your tacks can get a good grab and don't fall out. I went with 1/4" thickness and have had good success with my manual pinning! :-) Just think about how many cork boards you would have to hang up to have your Pinterest boards live and in person.