Six companies can also refer to the Chinese Six Companies
Six Companies, Inc. was a joint venture of construction companies that was formed to build Hoover Dam and later went on to build Grand Coulee Dam and other large projects. It was a consortium formed by six smaller general contractors in order to submit a bid for the Hoover Dam contract. Because of the immense size of the dam, no single contractor had the resources to make a qualified bid alone. Harry W. Morrison of Morrison Knudsen (Washington Group International) formed the joint venture and was elected president of it. Frank Crowe, an employee of Morrison Knudsen was the General Superintendent. Six Companies started working in about June 1931. Six Companies was composed of:
The dam was completed two years early, after a bid of $48,890,955 ($711,604,200.81 inflation adjusted). The project was so complex and large in scope that only 3 bids were received. Six Companies bid was $5,000,000 lower than the next highest bidder, a bid spread of almost 10%.

Morrison-Knudsen of Boise, Idaho 10%,
Utah Construction Company of Ogden, Utah 20%,
Pacific Bridge Company of Portland, Oregon 10%,
Bechtel Corporation of San Francisco, California, and Henry J. Kaiser of Oakland, California, (Bechtel-Kaiser) 30%, and
MacDonald and Kahn of Los Angeles, California 20%, and
J.F. Shea of Portland, Oregon 10%