I have been thinking of getting a guitar slide on ebay. I have never used one before and I am worried my finger won't fit, and it will fall off. Do they come in different sizes or is it one size fits all?
yes they come in diff sizes
they are usually made of glass or metal and will obioulsy wound diff
i take it you cannot buy locally. they are not expensive.
if you are unsure, maybe go to a local jewelery store and have your finger measured as if you were buying a ring. not sure if that corrolates to a slide but it might help.

hope that helps....

Go to a shop and buy there.
R.I.P. My Signature. Lost to us in the great Signature Massacre of 2014.

Quote by Master Foo
“A man who mistakes secrets for knowledge is like a man who, seeking light, hugs a candle so closely that he smothers it and burns his hand.”

Dude its measured using ring sizes, so find out what what ring size you are and buy the slide that fits your finger.
P.S. Buy new slides don't get used ones
Cant see saving much money on ebay as the last slide I bought new was all of 5 bucks at the local store.