So long as you have the right crimp tool it's not too much of a black art

It's not so much the crimp tool, it's making sure you use the right kind of RJ45 connector depending on which type of cable cores you have (solid or stranded).

If you use a connector designed for stranded wire on a solid-core wire, it will seem to work for a while, until later, when you start to get intermittent failures that are very hard to trace.

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Tony Fabris