Finding the size on circular needles

Hi. I’m new here and am very confused. My name is Linda and I live in Arkansas. I am wanting to knit some caps for Christmas presents and the patterns I’ve found use circular needles. I bought a box of knitting needles at a yard sale several years ago and there are lots of circular needles in the box, however I can’t find a size on them anywhere. How do I tell the size of the needles? And is there any secret to using them?
Thanks,
Linda:woot:

Many circs (many needles, period) are not marked with their size. The fastest way to tell what is what is to buy a gauge.

You can use circulars to knit items flat, just don’t join the stitches. There’s videos that show how to knit in the round on the Advanced Techniques page.