TweetHey bro,
Yeah, you can use them, but 21g are too big for me. I use 25g 1" pins in glutes and thighs. Also you don't have to rotate both glutes and thighs for 2 shots a week, you can do just glutes, or just thighs. Get some smaller pins, less scar tissue and they are so easy to get. Look at the thread about trusted friends for some good people.
Good luck,
Skarn