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?

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.