Allted's springy pen holder for the Mostly Printed CNC is a model of simplicity. But I didn't like the idea of having to cut zip ties to switch pens on my MPCNC. So I replaced the pen side with straps using M3 screws and nuts. The nut traps are likely to mess up a bit while printing, but just tighten up the screws to pull the nuts into position.
You can customize the maximum pen diameter (default: 18mm), and with long M3 screws, you can go as thin as you like.
There are two versions: one has shorter bridging but more 45 degree overhangs.