I designed this for the Microsoft Band.

It is a standard that fits the magnetic loading cable. I redesigned the uploaded model to correct the flaws I noticed when I printed the first revision,

The cable should be inserted by getting the USB plug through the rectangle at the top first. Then you try to bend the magnetic plug in so that the band holds the connection. This should be visible on the picture. In this redesign it should be easier to install and remove the plug, but i;m not sure because I did not print it.

It may be hard to get the magnetic plug in, and even harder to get out. I use it as a permanent charging station.