How is a Stop Order different than a Stop-Limit Order?
A stop order is activated and becomes a market order once the stock trades at or through the stop price specified by you. Once the order is activated, you are guaranteed execution, but there is no guarantee of the execution price. The stop price designated in a sell stop order must be lower than the last sale price by at least $0.05; the stop price designated in a buy stop order must be higher than the last sale price by at least $0.05.
A stop limit order is similar to a stop order in that a stop price will activate the order. However, once activated, the stop limit order becomes a limit order and can only be executed at the limit price specified or at a better price. You are therefore not guaranteed an execution with a stop limit order. The limit price designated in a sell stop limit order must be equal to or lower than the stop price; the limit price designated in a buy stop limit order must be equal to or higher than the stop price.