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I bought a Ruger 10/22, my first rimfire gun, and it came with a small rail that can be screwed on top of the receiver. It's smaller than the rails I'm used to.
How am I supposed to know which rings or aiming device will fit on it?
Yes, this might be your best best because the rail that comes with the ruger 10/22 is a TRUE Weaver, and only (to my knowledge) works for rings and accessories that are Weaver brand with the narrower cross channels (0.15").
Weaver / Picatinny (I have no idea WHY they use the word weaver here) has the more universal wider channel (0.18" "weaver" or 0.206" picatinny) for mounting.