How do I attach a jumpring to a magnetic clasp? Once the ring is open, it is hard to get it back together securely. Is it necessary to use jump rings for certain clasps? I haven't been using them with other clasps...
The use of a jumpring with your clasp depends on your own personal preference.
If your design preference includes jumprings, check that the gauge of the jumpring is suitable to the weight or the pressure the jewelry is putting on it. Jumprings of lighter gauges (20-gauge and higher) should be reserved for more delicate jewelry and lightweight components. Sturdier gauges (18-gauge and lower) can bear the weight of heavier beads and designs using large gemstone or metal beads.
When jumprings are used, make certain they are being opened and shut properly: with a twist, not a pull. Jumprings which have been pulled apart to open, rather than twisted, are difficult to reclose snugly.
Finally, if jumprings just aren't fitting together snugly, no matter how much you try to bend them back and forth, you can try the loop-closing pliers to close the jumpring tightly.
Once the jumpring is closed, adding a drop of instant glue to the seam provides additional security. Jumprings are not closed seamlessly unless they are soldered together. You might also consider using split rings (think of key rings). They are slightly more difficult to use, but much safer and more effective.
In addition to using jumprings to attach your clasp securely to your design, you can use a double simple loop or a double-wrapped loop.