Originally Posted by USAZorro
When looking for frames - especially with older or very neglected frames, there might not be a nice sticker telling you what the frame is made of. Obviously, one would first ensure the frame is sound, but presuming that it is, look at the right rear dropout. If it is stamped - it certainly is not a high quality frame. If it does not have a separate hole for a derailleur to attach to, it almost certainly is not a high quality frame. If it has an adjustment screw (or the hole for an adjustment screw), it is almost certainly at least a mid-level frame (ie - not junk).
I've heard this advice on dropouts is very good, but how exactly do you tell a forged from a stamped dropout? Are all "slotted" dropouts stamped? Because I have a Trek frame with slotted dropouts, but they're not flat, they have curved surfaces, and so I'm thinking they must be forged.