Side-light Fiber Optic Tube - 4mm Diameter - 1 meter long : ID 4163 : $7.50 : Adafruit Industries, Unique & fun DIY electronics and kits
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Amazon.com: Sumnacon 5pcs Banana to Banana Plug Test Lead Set, 4mm Stackable Banana Plug Wire Test Cable Lead for Multimeter, Electrical Test Wire 1000V/15A : Industrial & Scientific