I'm not a big fan of using all-thread or threaded rod, but I've had to use it at work the last few days. I am trying to take off a destroyed gearbox from a piece of equipment useing a port-power. The shaft the gearbox is gaulded to is 5 inches in diameter. Point is, I'm useing two pieces of 20mm threaded rod and a 50 ton press to take off the gearbox. I ordered 4140 rod, which McMaster-Carr calls B-7 rod. I've had the prota-powered maxed out several times and the rods haven't even stretched. Normal hardware store rod is like bublegum and would have broken quite easily. If you have to use threaded rod, go for the 4140 stuff.
The yield strenth of B7 is probably twice that of hardware store all thread. B7 threaded rod is cut to length for flange bolting in power and process plants. The gaskets are typically spiral wound stainless steel chevron with a filler like grafoi or teflonl; very, very hard to seat, but gives an extremely tight and durable seal. You want 2H heavy hex nuts to go with the B7 if you need nuts.
The Jalopy Journal
