A lot of companies used "House, or Captive" thread sizes so that when you needed a replacement part, you would buy from them. Brown and Sharp used the same system, but used standard thread sizes but higher thread profiles. I worked for Merrow Machine Company, a manufacture of high speed over-seam industrial sewing machines. All of Merrow's threads were their own sizes, and when people needed replacement screws there was a lot of profit to be had.