This part holds two acrylic rods against the power and activity status LEDs of a Raspberry Pi 3 B+. The acrylic rod "routes" the light just like edge-lighting an acrylic sign,
I used 1/16" acrylic rod I bought on Amazon. http://a.co/82z48mN
This part fits tightly in to the screw hole of the Pi between the status LEDs and the microusb power plug.
I'll plunge the other end of the acrylic rod through to the outside of my custom case and sand it smooth.
This part was specifically designed for a Raspberry Pi 3 B+, though I imagine it will work for any Pi except the zeroes.