Maggie Thatcher was right wing but shook up the established order. In the true sense she could not therefore be called conservative. She was the proponent of change in her time. (see also Hayek, who wrote an essay "Why I am not a conservative"). A contemporary, Leonid Breshnev, was left wing but also determined to prevent change in his country. He could not therefore be called a progressive. He was against those calling for change.
Regimes of the Right and Left have been variously militaristic or pacifistic, nationalistic or internationist, expansionist or isolationist. So what is the difference between left and right, and what is extreme left and extreme right?
The difference is essentially one of economics: The right believes in the free market, the left believes in central planning. The right believes in planning by individuals for themselves and the left believes in planning by the State for everyone.
So what is extreme left? The answer is fairly obvious: Communism. The State owns (or directs) all the means of production.
So what is extreme right? The answer is not quite as obvious: Anarchy (used in the secondary sense of "self government"). There is no central authority.
That stupid "wheel of politics" which shows left and right extremes eventually meeting at the same point was invented by the Communists and, stupidly, taken up by Loser -er- Libertarians. It's not a wheel; it's a straight line from total government control to no government at all.
UPDATE: To give an identifiable example of an extreme right winger (ie zero-government, anarchist type of guy), here is David Freidman, son of Milton.