They are called Probore and have the threads at the muzzle end. I have seen them in 12 gauge, but can't find anyone, including Remington, that lists them in 20 gauge. According to the Remington website, the 20 gauge G3 uses Remchokes. "All models equipped with 5 choke tubes (ProBore® on 12 ga., Rem® Choke on 20 ga.)" Mark