Orders are used like STP orders, but execution is restricted to the limit price or better. They do not become MKT orders once the STP price has been reached. No order is guaranteed an execution.
Buy STP LMT is activated when the commodity is bid or traded at or above the stop level; the order is not filled unless the price remains at or drops below the limit level.
Sell STP LMT is activated when the commodity is offered or traded at or below the STP level; the order is not filled unless the price remains at or rises above the limit level.