Hey Sylthecru,
when I watched the video that your link contains, I get an idea how people manage to fit a 12 mm cable into a flimsy “aviation” connector with a 7.8 mm strain relief – they don’t! I wish nobody would need to do such unserios things, but instead bought spindles with serious connectors.
The best thing is always to buy the spindle cable manufactured by the spindle manufacturer. All reputable spindle manufacturers offer this.
Also serious spindle connectors, like all high power connections, are never soldered, but crimped, or clamped with wire ferrules.
Anyway, be sure to fulfil the requirements described here:
The PE wire has to be connected to the fourth pin on both sides (crucial for safety) and the cable shield must be connected to connector housing(!) at the spindle end, and the other end of the shielding must be connected to the VFD control cabinet earth plate on the VFD’s end. Always connect ground and shield at both ends!