This is something I've been trying to figure out too.... I recently entered several trades usint stops. Usually with a limit, price must trade 1 tick above/below ur limit price. If it is a stop, then u can be filled if price trades at ur stop price, but not 1 tick above/below.
In my backtesting, I want to enter above/below the signal bar, I should use a limit instead of a stop, because sometimes I'll get filled and the market won't ever penetrate the entry bar low/high (especially in ES), therefore a stop *might* get filled, but a limit won't.
My broker OEC.