I use these which were on special offer a couple of weeks back for about £20 the set. I needed to make some little aluminium sliders to adapt them for my 3/4" track, and for the clamp bars I just use scraps of ply, hardwood, or whatever comes to hand and fits for any given job - just bang a 7mm hole in the appropriate place, dig out some packing, and away you go. But it depends on what you're clamping and cutting forces involved, of course.