These mandrels are not hollow like the others sold here , weight 150gm
 
Make the size and style jump rings you need. Simply wrap the wire around the notch in the size you need, squeeze ends together and cut the wire if you are making jump rings, twist it together for loops.
Will make 1.5mm up to 10mm rings.
 
Small mandrel 1.5mm -5mm
Large mandrel 6.0-10mm