Use the torch to form a ball on one end of the 20g wire, then quench it in water to cool. Slide your bead onto the wire and gently push it up against the balled end.
Holding the bead safely away from the flame, use the torch to ball the other end of the wire.
When quenching this second end, dip only the newly balled tip into the water-if the bead has gotten warm, submerging it too quickly could cause it to crack.