Pictures...

http://images.google.co.uk/images?hl...ap&sa=N&tab=wi

Suppliers...

http://www.google.co.uk/search?hl=en...et+strap&meta=

Wrap it round both sides of the bar so that when you tighten it up, it pulls the ends together. I'd get the big ones so you have a good strong ratchet that you can get lots of leverage onto.