#1 grease has an NLGI grade of 1 and is a semi-fluid grease with a consistency similar to peanut butter. It is often used in automotive applications such as wheel bearings and universal joints due to its ability to flow into tight spaces and provide protection against wear and corrosion. #2 grease has an NLGI grade of 2 and is much thicker than #1 grease. It has a consistency similar to soft butter or shortening and can be used in high-load applications such as ball joints or fifth wheels due to its superior load-carrying capacity. Both are suitable depending on their properties, different types of applications, and whether or not you need more thickness or higher workload capacity.