Hi, could I ask what size/length of rivets are used when fixing a aluminium floor and the side panels to the underside of the chassis.

Iam using 4mm 10mm on the top of the side panels which is 1.2mm thick and my floor panel is 3mm so and have been told to use 13mm, if I intend to rivet through the side panel and the floor in one(3mm+1.2mm) what length rivet is used??

Thanks again

Jools