Ahh right I see
When I fitted my seat (only the one :wink: as otherwise the mrs will want to come in the car too) I used the following
4 M8 x 40mm cap headed bolts (12.9 tensile with allen key head)
4 M8 washers
8 M8 penny/repair washers
I also bought nyloc nuts but used the original Renault nuts too then wound the nyloc nut on afterwards
The above is per seat so will obviously need doubling up if you're fitting 2. I put one of each washer on top of the subframe and also used a penny/repair washer underneath too, I do like a spot of overkill when it comes to seats/harnesses to be honest
I can mock one up in the morning if you like as I have a spare subframe, just so you can see what I've done