Why can I only trade a maximum of 5,000 shares in NYSE and AMEX securities?
It is simply more cost effective for you. Any trades that exceed the trading limit of 5000 shares would be subject to an additional charge of 1.5 cents per share. This would equate as a commission equal to the normal rate (17.50 + USD3.00) plus the additional charge of at least USD75.01 (5001 x USD0.015). By placing trades that are limited to a maximum of 5000 shares the commission would be a maximum of 17.50 + USD3.00 per 5000 shares. Therefore, it is more cost effective for you to enter two orders and incur commission charges on both trades than to trade over 5,000 shares at one time.