Ive snapped a few of these on my 511, i replaced them with (54208 fluorine coated ball studs), the thread is slightly longer which can be used to put spacers underneath and provide an extra tuning aid, or if needed simply cut down. But they are much stronger and i have yet to break one.
We have these in stock and can be found by clicking here -
http://www.jtmodels.co.uk/prestashop...?id_product=87
Hope this helps.