How do you know what size thread to use for a necklace strung with knots in between each bead? I have had experience with the beads slipping over the knots.
When knotting pearls, it is likely that freshwater cultured pearls will have much smaller holes than glass pearls or Swarovski crystal crystal pearls. Try a B or C silk thread with freshwater pearls and an E or F thread with manmade pearls.
Different types of thread have different numbering or lettering systems. Generally, the lower the number or letter, the thinner the thread. For example, silk threads run from 00, the thinnest through FFF, the thickest.