Instruction HERE ( youtube.com/watch?v=00g-Wpr8tMw ) I hope this helps!

The Romeo Zero will not fit the P320 models. The P320s are milled for Romeo1 and Leupold Delta Point red dots and the thread pitch is different. You can buy adapter plates for other optics, but the micro dot Romeo Zero wouldn't make any sense on a full size pistol.

Garry, Sig Sauer Romeo 1 installation video here : youtube.com/watch?v=xokojLLec0g

This comes milled for the Romeo Zero foot print, you just need a bit that will fit the screws, the optic, some blue loctite, and I always use a torque driver for precise tightening on optic screws.
I have this one
budsgunshop.com/product_info.php/products_id/50682