I agree with janikphoto and kevlar.
Tapco is the best for sks mags. but best using the 10 round fix'd with stripper clips ... I know after spending a bunch of money on clips that fail all the time, tapco works the best. 20 rd'rs are tough to find at the moment, a lot of places sold out of them or on back order
also if you or anyone can get your hands on a fix'd 20rd'r, get it. I have one on 1 of my chinese sks's, came with the gun when we bought it. Works great as well and it takes stripper clips!!!