Combines Removing wires

likely not a big problem in corn. In grain, the straw will spear into the holes and can eventually plug the concave reducing seperation. The best plug kit is from AGCO. Part n 71371547. It has enough plugs to do 250 holes. You will need around 150 for a R52. These are 2 pc. plastic plugs that you snap in from each side. Bit of a pain to install but they don't fall out.

how about using boltsIJ

Really!IJ they have a kit to fill the holesIJ We have left ours open! I did not notice much wheat straw in the holes, but I had straw bent over and hanging from the rods in ours. I will look closer. Oh great, I hope my wife doesn't see this either!

Bolts will be difficult to put in, and will stick out (remember 150 of them) restricting seperating capacity. The plugs from AGCO are almost flush with the concave bars.