I wouldn't use anything smaller than a 25 ga in my delts or thighs simply because the muscles are large enough to not be damaged. But I think an insulin pin would be good forf site injecting into smaller muscles but only with smaller amounts ie if you had to inject say 1ml of fina you could hit your left and right bicep with a half ml each and this way you could have more sites and less damage which would equal more ml per week.