IAD/IAS/IC/NAD coaster company

I've been wondering about the history of these coaster companies for a while:

International Amusement Devices, Inc.,International Amusement Service, Inc., International Coasters, Inc., and National Amusement Device Company.

Are these all the same company, only under a different name? Why didn't they build many coasters (especially IAS)?
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Don't look down-Oblivion
SLCs kick arse (when smooth).

i know both colossus in sfmm and la montana rusa in mexico city were built by iad.

NAD build Big Dipper at Geauga Lake with the help of John Miller.

NAD, IAD are the same (I'm not sure about the others)

I emailed the NAPHA ( http://www.napha.org ) a while ago (wanted to find out more about the Big D) and they said they went out of business in the 80s.
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My fellow Americans, let's roll!
I pray that I will never see a Six Flags Conneaut Lake

*** This post was edited by bigkirby on 11/21/2001. ***

National Amusement Device was originally founded as the  Dayton Funhouse in the 1920's by Aurel "Dutch" Vaszin , supplier of various amusement rides and equipment. NAD built some really spectacular coasters, many designed by John Miller. Sadly most of these rides no longer exist. In the 1980's the company was purchased by Bill Roose, son of George Roose of Cedar Point fame.The name was changed at that time to International Amusement Devices. From this point on they seem to have specialized in park design and the brokering of rides.