bolt. im pretty sure someone knows a link with a guide that shows how you do it. you have to like put self tapin screw in, then clip them together and stuff. other people use tiger seal, which is a type of strong glue stuff.
if they the gsi skirts they clip on, but only the gsi's have the pins that the plastic clips go onto, if they are gsi ones id slot the pieces togethor glue them on using tiger seal and use paper masking tape to hold them on till the glue sets