I had an opportunity to find some excellent deals on camlocks recently, and so investigated my options fully and recently purchased a suite of them from ProFlow Dynamics. A bit of research shows their prices to be about as cheap as it gets; bargainfittings.com has some comparable prices–some more expensive, others less expensive–but didn’t have expedient shipping options.
Supposedly, the barb portion normal C-type camlock has an outer diameter (OD) of approximately 1/2″, in order to easily accommodate the 1/2″ ID of selected tubing (I recommend thick-walled thermoplastic tubing to avoid collapsing when used with a pump). Therefore, it would only make sense that the normal C-type camlock would have a greatly-reduced ID. I think the picture from the Homebrewtalk forum clearly demonstrates the difference.
Despite the larger OD of the “C Special” camlock, I was able to force 1/2″ ID thermoplastic tubing on to it with a little muscle. No boiling necessary. I’ve read that, with the stretching needed to fit 1/2″ tubing on the “C Special” camlock, no further device is needed to avoid leaks. Nonetheless, I was able to squeeze a small stainless steel worm clamp (albeit with great difficulty) in place.
In some anecdotal testing, I found the flow rate for these camlocks to be exceptional. I replaced a 1/2″ hose barb—which was really 1/2″ on the outer diameter, and quite a bit smaller for the inner diameter—and experienced quite a bit higher flow rate.