This is a grommet I use for my light boxes, the pictures show how to use them.

You will need to create a negative part cylinder in your light box with a diameter of 13.5mm that works well for me.

I then use a glue gun to secure them inside the box with the cable so they cannot be pulled out.

The grommets are a tight fit and you may need a thin rounded piece of wood or something to ease them in so they sit correctly,

but once in correctly they can be rotated round do the gap is at the bottom for a neat finish.

The texture from your pei plate I usually ensure are facing out so it matches the outside face of the light box.

I print these in 95a TPU using the external spool and have no issues with it using the settings with the file.