My beautiful new Ogre is studded all over with braze-ons. I know what a braze-on is -- a predrilled hole in a bike frame to attach racks, packs and accessories. But I don't understand how they do what they do. I've Google-searched "how do braze-ons work" and variations thereof, but it was no help at all. Apparently this is something I'm supposed to already know.

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I thought the silver cap might screw off like a cap nut, but no. Do you drill the screw right through the cap and mount, say, a bottle cage that way? I'll probably take it to my LBS for any big attachments, but I'd hoped I could at least mount the bottle cage on my own. What do you suggest?