This is a simple model inspired by the Secretlab Magnetic Cable Anchor that is used for the Secretlab Magnus desks to anchor cables to a metal surface. I never purchased any of the original anchors so I did my best guess at dimensions and made sure the inner tunnel was able to support various cable ends without them slipping through (Apple's Lightning cable being one of the skinnier cable ends). I attached two 20x5x2mm magnets (one for each side) with glue after print completion.

I also created a double tunnel version here.