Originally Posted By: Spooled
The side with the cutout half circle (shown in the picture) goes against the drain plug. It will screw onto the plug. They work fine, but a torque wrench will make sure it crushes properly. Nissan uses this type of washer.
^^This^^ I just replaced one on my Frontier. I reused the one that came on it for the last three OCIs. I didn't think it mattered, but it only went on completely one way. The notched side goes toward the plug. It was a bear to get off the old one too. I would go a different route but it came with the OEM Nissan filter.