For solos, Betty era stuff particularly was largely rack rather than pedals. TC Electronic 2290 delay, Korg SDD-200 (I gather that one goes way back to earliest recordings), Digitech DSP-5. Yamaha GEP-50, too. I have the latter, and the early reflection reverb and subtle (i.e. a couple of cents) pitch shift on it are instant Helmet solo. Anyway, I think a lot of it is delay and reverb with such short times that it sounds a lot like a chorus effect. The "Heavy Metal" pre-set on that thing was the default Strap It On rhythm tone, too, I gather, and again... it's instant Blacktop.
I'm pretty sure current rhythm sounds are pretty much all amp distortion. The tone is unmistakeable. My Fryette Pittbull with the gain whacked up sounds exactly like Size Matters, Monochrome, etc. I recall Chris T and possibly Dan using Tube Screamers and variants thereof, but the overall characteristic of the tone is pure Fryette.