captive nuts ?

taken mud flap holders off and need new nuts the ones fixed in the cross member, i think they are called captive nuts. any idea where to get them and what size would i need or lr part no even better. will i need to redrill holes to fit new ones .
thanks.

They are called rivnuts - the size you need are M6 - you knock the old ones into the cross member using a punch and fish them out the ends.
To fit new ones either buy the tool or use a longer bolt with a couple of nuts on winding them to compress the rivet part of the nut - they work in a similar way to a pop rivet.
loads available on ebay or you could go to a fixings supplier (nut & bolt shop)