Nylon PA66 is a strong, stiff nylon with good chemical resistance and heat tolerance, well above PA12 in strength and stiffness, though it absorbs far more moisture.
Nylon PA66 is a stiff, strong engineering nylon with good oil and fuel resistance and a heat deflection of about 180-200 °C under light load. Under heavier loads it softens at much lower temperatures.
It absorbs moisture (about 2.5-3.5% at normal humidity, far more than PA12), so parts swell slightly and lose some strength and stiffness when humid.
Nylon PA66 is a strong choice for stiff, heat-tolerant parts such as brackets and housings.