allen head bolt size for brake caliper

I'm putting brake pads on my 99 astro awd cargo van. It looks like the bolts holding on the caliper are allen heads. Does anyone know what size these are? I have to go into town and buy the right tool. Is it a 3/8 ? Also, Do I need the C clamp or can I get by without one?

Thanks.

Eric

The size was indeed 3/8 hex wrench. They were really on tight and couldn't budge them so I used a hydraulic jack to apply force to the hex wrench and it worked like a charm.

A dab of anti-seize on the threads will prevent that in the future.

I did my front brake pads on my 1997 Astro yesterday, and I too can confirm a 3/8" allen wrench works for the caliper removal. I would have thought it would be metric since everything else is metric, but whatever. Love disc brakes; it takes longer to remove the wheel than it does to replace the pads. Today we tackle the rear brake shoes...they're never as easy as disc brakes.