There are a number of ways of attaching the pendants to thread of any thickness. On pendants with small holes or loops running from front to back, use either a jump ring or a bail. The thread can pass through this, leaving the pendant hanging correctly so that it sits flat on your neck.
If the hole runs from side to side, two jump rings are needed for the pendant to hang correctly. A finding called a bail and loop could also be used, but check that the size of the loop is big enough for the Thread .Open one jump ring, using round-nosed pliers and join it to both the pendant and the other jump ring. Close it up again with the same pliers.
Open the jump ring with a pair of round nosed pliers. It is important not to leave any gap at the join on the jump ring. Opening the jump ring sideways will help. Re-close the jump ring with the pendant attached.
When using bails, squeeze the looped bail tightly shut, with the prongs through each side of the hole on the pendant.