A. Regulation T sets the minimum percentage of the payment you must make when you buy stock on margin. The FED has a higher margin rate through Regulation T which means that it can control over speculation in stocks and stock market credit. It prevents another stock market crash. It will rise if there is a bullish market and go down if it is a bearish market. Regulation T is important to margin buying because Since January 1974, the Regulation T has been set at 50%.