Great to see the Potts flies utyer. My father and I used the Sandy Mite and the Lady Mite pretty much exclusively on the Big Hole River and Rock Creek back in the sixties. Very popular fly here in Montana. We swung them and sometimes added lead if we had to. They came from a time when durability was premium. Delicate flies didn't cut it with my dad. As I recall, Potts used chinese boar hair - not elk - and they would really last. I tied some years ago, but they take a lot of time to do them the way Potts did them. I can't tell you how many fish they accounted for.
A friend of mine bought all of the chinese boar hair from a Butte Montana shop some years ago as it became impossible to get the right stuff.
When we didn't have enough money to buy them ( I think they were 45 cents), we would buy a knock off fly called the Black Bear Brown and the Brown Bear Black. These woven flies worked too, but I never fished them as confidently. They were 10 to 25 cents. Sometimes I could dig a dime out of the couch. I still have a couple that I tied, but I won't fish them.