My "Solo" clamps could hold the Queen Mary. IMMENSE pressure if you are goofy enough to exert it. I 'spread the love' with a packer much wider than their heads and have no problem with glue ups; they REALLY squeeze out glue and close seams. That said, their real boon is in clamping up sumat in the correct registraton one-handedly, while you hold two slippery wotsits in the right orientation. Thereafter, I get a few 'F' clamps distributed around a perimeter, or whatever is needed. Mine are approaching 10years old - and perhaps more - with no signs of slippage/wear unlike the absolute ashtray-on-a-motorbike ones with the serrations on one side..yuk.
Sam