Since slides themselves were mentioned, these are the three that have worked best for me over the years.
L-R:
This was a piece of steel pipe that I turned both the I.D. and O.D. on a lathe until it fit comfortably on my ring finger. I use this on my Dobro or acoustic guitars. I like the sound of a hefty piece of steel on acoustic guitar strings.
A Stevens Steel which gets used on my lap steels.
The good ol' Coricidin bottle for electric guitars. It was tough finding one that fits on my ring finger. I found a second and bought it to have a spare.
I like using the slide on my ring finger because I found that by using the index or middle fingers to fret behind the slide and the pinky to fret in front of the slide, I have many options for making chords when in open tuning. I usually use open D or E depending on the guitar (because I'm a Duane disciple), and it's easier to be able to make minor, 6th, and diminished chords that way.
These are a mix of cast offs, gifts, or experiments. The two chunky glass ones are good to use on my ring finger. A friend gave them to me because they were too big for him. The narrow glass one barely fits my pinky. I should maybe give that one to my friend. Then the steel one on the right is a bearing race. I thought it was pretty comfy on my pinky, but found it a bit loose. It doesn't fit my ring finger though. It stops at the knuckle. I have a bunch more in a cookie tin.
