X2 sets of the units that hold the adapter plate to the slide ~ $20 per set 

And x1 set of screws to hold the RMR in place to plate ~ $20 for the set 

I have four screws that would output two pistols on the adapter plates, and I have one set of screws to hold the optic on the plate

it is a little confusing. I did order these on accident, but they sure are sharp. I included some pictures of my pistols mounted so you know what I'm talking about.