Back in 1911 the Farwell Company of Chicago got tired of paying 50 cents over face value per coil of 3000 stamps from the Schermack Company. They embarked on a mission to develop their own perforation that would still work in the Schermack mailing machine. After a few trails they decided on 2 sets of 4 holes. This would still allow the mailing machine to operate without infringing on Schermack's patent.
They bought the imperf stamp sheets at the local post office, perforated and then coiled them. They must of had a heck of a lot of mail for this to make economic sense. lol
Here is a single sample.