I normally use brass on acoustic and glass on electric but I will play glass on acoustic as well. I never play brass on electric though bc the weight of the slide is too much for the lighter electric strings (in my opinion). I normally wear the slide on my ring finger. I sometimes play with it on my pinky but it just doesn't feel right to me even though it allows me to use my fingers with more ease. I have an old glass slide that was Duane Allman's slide that I use pretty frequent but it is a bit small for my finger. I also have an old medicine bottle I found at the Merle Travis birth house years ago. I like it the best out of all of my slides. I am not sure what the brass slide is that I play with. I have had it so long I can't even remember where or when I got it. It is tapered and feels really good. Actually I like it better than the medicine bottle when I play my National steel body. On every other guitar though the medicine bottle wins. I have no clue what kind of bottle it is because when I found it there was no label or anything on it. Just a plain glass bottle with no markings or anything on it.