The deep groove in a ball bearing is characterized by a raceway with a deep, concave profile that forms a continuous, circular track for the bearing's rolling elements, typically steel balls. This design feature allows the balls to move freely within the raceway, distributing the load evenly and minimizing friction during rotation. The deep groove also provides space for the lubricant, which helps to reduce wear and heat generation, ensuring the bearing's longevity and reliability.

In summary, main bearings are primarily responsible for supporting the rotational motion of the crankshaft and withstanding radial loads, while thrust bearings are designed to counteract axial forces and maintain the axial position of the crankshaft. Both types of bearings play critical roles in ensuring the smooth and reliable operation of engines and machinery.