I was careful when I used the notch coil. Many people were saying the leads broke easily. If you center the leads in the middle of the grub screws, it helps. If they get moved to the top or bottom of the screw, the threads will pinch the wire against the metal post and cut the leads. If the leads are centered then the flat part of the screws will just smash the wire without cutting them.
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Not necessary broke by the screw, sometime it broke at the other end, the lead simply disengage from the coil, this could happen if one try to bend the lead too much.
My way is to tighten both leads in turns. It takes me a few rounds to fully tighten both ends, this also means the coil won't go out of "proper posistion" too much, thus required only a slight adjustment in its position after it has been fasten on the poles.