Volvo: luggage rack installation, machine bolts, rubber cone

Question
I purchased an original luggage rack for an old 240 wagon.  I was getting ready to install it.  It looks like the bolts that came with it are machine bolts.  I was planning on drilling into the roof but it looks like these bolts would need a bracket or something (vs drilling into the roof sheet metal)  Any ideas?

Answer
The machine bolts go into a nut that rests inside a rubber cone.  The holes are drilled in the roof of the car, and these rubber cones (about .5 inch long) are droped point first into the hole, so that only the bottom portion is showing, where the nut is exposed.  You then put on the roof rack and screw in the machine screws to these nuts.  When they catch and tighten, they draw up and squeeze tight the rubber cone, securing the rack and creating a water tight seal at the same time.  Actually works quite well.  You'll have to buy a new set of rubber cones/nuts from a deal, but they are only a buck or so a piece.  Good luck!