Router guide you for use with the flex shaft (and clones).

One normal version and one with a flat side so you can squeeze it into awkward spaces. I use it for putting notched holes in Bud Enclosures with a flush trim bit.

Don't try to use the guard ring to mount and unmount it, the spurs are not that tough and it will probably break.

As usual, no guarantee's this will work, use proper safety gear, may combust spontaneously.