I would suggest going for a block type nut as mounting a round nut is a little bit more tricky.

Below is some pics of the ones i make for use with M8 Threaded Rod:







The above image is how they look in my ebay shop at £4.99 each with fixings. £15 will see you get all 3 nuts + fixings via Royalmail First class.

You can read how well they work here, [ame="http://www.mycncuk.com/forums/showthread.php?t=586"][/ame] let me know if i can help you.