In RC car shocks, "wt" and "cst" both refer to the viscosity of the shock oil used in the shocks, but they use different units of measurement.

"wt" stands for "weight" and is typically used to measure shock oil viscosity in the United States. The weight measurement is determined by the rate at which the oil flows through a specific size hole at a particular temperature. For example, a 30 wt oil flows faster than a 40 wt oil through the same size hole at the same temperature.

On the other hand, "cst" stands for "centistokes" and is used to measure shock oil viscosity in the metric system. Centistokes is a measure of fluid viscosity, based on how fast a fluid flows through a narrow tube. The higher the number, the thicker the oil. For example, a 300cst oil is thicker than a 200cst oil.

While both "wt" and "cst" measure viscosity, it's important to note that they don't always directly translate to each other. A shock oil with the same "wt" measurement as another may not have the same viscosity if measured in "cst" units. As such, it's crucial to use the proper viscosity measurement units when selecting shock oil and to refer to the manufacturer's recommendations for the correct weight or cst oil for your specific RC car model and driving conditions.