Kuhn, Markus: International standard paper sizesUniversity of Cambridge. 13.7.2018. Viitattu 8.8.2019. (englanniksi) Lainaus: "Not specified in ISO 838, but also widely used, is an upwards compatible 4-hole system. Its two middle holes correspond to ISO 838, plus there are two additional holes located 80 mm above and below these to provide for more stability. This way, sheets with four punched holes can also be filed in ISO 838 2-hole binders. This system is also known under the nickname "888", presumably because the three gaps between the holes are all 8 cm wide."
