Apparently, sash clamps are not a thing in the U.S. I haven’t been able to find any, except on Amazon, and they are imported from the U.K. with a hefty shipping charge. Pipe clamps, however, are everywhere and I can pick them up cheap at Home Depot along with various lengths of pipe. Are there any functional advantages to sash clamps over pipe clamps that might be the reason why Paul uses them?
I get the ones that Paul uses at Harbor Freight. The 24″ are 9.99$ regular price and are often on sale. I believe Paul has a video about strengthening them with a bit of wood in the rail and adding plywood to the jaws. I haven’t regretted these in the least. I was able to get 5 of them for the price of one Bessey.
Pipe clamps are stiffer and more versatile than the flimsy aluminum “sash” clamps at HF. The latter are lighter and can be stiffened by stuffing them with wood as Jim suggested if you don’t mind doing some extra work. Prices are similar.
Iron sash clamps are stiffer than either of the above. They are also heavier and far more expensive.