Frank Gilbreth went into business for himself on April 1, 1895, after almost exactly ten years with Whidden Construction. Whether this move was planned and inevitable or whether he exercised the option he reportedly stated at the beginning of his association with Whidden because promotion to partner level was not forthcoming is a matter of interpretation of the various tellings of the story.
The primary construction company was always “Frank B. Gilbreth” followed by various trade names, including “Mason” and “Builder.” By about 1900, he had settled on “General Contractor” and that full name appears in nearly every ad, billboard and reference. It may or may not have been incorporated, but “Inc.” was never used as part of the business name.
The main offices were located at 34 W. 26th St for many years, until that building (the Knickerbocker) was torn down. The remaining years were spent at 60 Broadway.
Most references say the management consulting firm founded in about 1910 was “Frank B. Gilbreth, Inc.” and that this firm was renamed by Lillian after Frank's death to “Gilbreth, Inc.” Some writers use the latter term for the entire consulting era business, and even the contracting company, but this is believed to be incorrect.
Several of the very late projects and ads use “Frank B. Gilbreth, Inc.” as the business name for contracting work, but it is not clear when this name was implemented over “Frank B. Gilbreth, General Contractor.”