Item #3 is only .66-inch in diameter, so it is too small/lightweight to be a hem/curtain-weight. It is what we relic-diggers call a "Longjohns" button, because they've been seen on nondug specimens of antique long underwear. But they were also used on pants-flies.
Other people call them simply a "4-hole button." Speaking of that... item #3 has four holes for sewing it onto the clothing. Hem/curtain-weights tend to have only two holes for that.
These thin stamped-sheetmetal 4-hole "Longjohns" buttons have been around since at least the 1840s, and were used on both civilian and military-issue underwear and pants-flies. For educational purposes, see the photo attached below, which show a World War One era version issued on US Army uniform pants. This version is made of zinc, and contrary to what some relic-diggers believe, is is absolutely not from the civil war. As the photo mentions, the larger version (about .66") says "US Army" and the smaller version (about 1/2") simply says "USA."