P means P-Metric. Usually found on cars and light duty trucks or SUV's.
LT means heavier duty truck. The LT tire is usually a stronger tire with more ply's. This thickens the tire side wall and tread pattern, pushing the tire chains sizing to the next larger tire chains.
If our sizes specifically say P or LT, you need to select the correct one. If we don't show a P or LT, just the tire size, then it fits both the LT and P version of that size.
For example, If your size is 245-70R-17 and we show only 245-70R-17 then it fits all types of that sizes P, LT and no designation. If your size is P235/75R-15 and we show a P and LT version, select the P version. If your tire size is LT235/75R-15, select the LT version.