I needed a grommet for a project that needed to have a slightly recessed m4 nut, so I whipped this up.  Pretty simple design, and prints in under 5 minutes.  The jacket for around the bolt had to be pretty narrow, also, allowing for only about .25mm of wiggle room.

Print in solid, concentric TPU at any layer height.

I also included a version that does not have the recessed nut.