All the proffessional stuff i see with crimps on them have the type of crimp that has no insulation like this:

All the ones i use have insulation on and frankly, are rubbish. I've experienced electrical failures before because of the crimps coming loose.
Looking at the way the wire is wrapped around the crimp looks very good quality and i want some of the action.
Does anyone know what these are called and what sort of crimping tool i would need? Also a good place to buy them would be much appreciated.
Thanks in advance,
Ringo