I'm not sure what the correct name for these parts organizers is. I usually call them "Tackle Boxes", even though that's not quite right. People tend to use them to store tiny screws and so on. I use them for electronics.
Today I designed little paper insert to go into them (in CAD), so I can label which electronics are which and find them more easily.
Sadly, US letter is not quite big enough to cover the whole box.
Printable PDF is available in A4 or in US letter. You can also see the SVG I was given originally which inspired this.
I recomment holding the paper in place with double-stick tape. If you don't have that, the usual trick is to roll normal tape into a small loop facing outwards.
P.S., to crop a PDF from A4 to US letter (assuming everything fits on both) without inflating the file size, use:
# Keeps all physical dimensions the same
pdfcrop --bbox "0 0 792 612" smallthing-on-A4.pdf smallthing-on-usletter.pdf