Those are pilot holes. Some people like to use various sizes of LEDs. The holes are intentionally "small". However, the placement was pretty critical, so we needed to put pilot holes or people would not ever get them properly set in the groove of the sine wave.
Drill to your preferred diameter and depth based on your LED diameter and how you like it to "shine". Some like theirs all the way to the front, almost protruding. Me... I like mine just into the back panel allowing only the light out of the front. So, I drilled mine to the point where the base of the LED 'stops' the LED from going fully into the hole.
Enjoy!
Edited to add - I also like mine with the small diameter pilot hole being kept at the same diameter at the front. So, I did not drill the larger hole all the way through the front panel.
I had a feeling that was the case. My dad has a drill press I can use, but the last time used it on an amp I didn't realize the chuck was too close to the side and ground a bit of it down. Hopefully nothing dumb like that happens to this beautiful front panel 🤞
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