When two solid blocks are in contact, their actual area of contact is generally very small. When non-conforming solid blocks with substantially different local curvature radii in the contact area are compressed together (such as spheres, cylinders, toruses contacting with flat surfaces, etc.), the initial contact area is small (ideally a point or a line) because of their geometry (Fig. 4.1.1a, b). Analysis of contact deformations between streamlined parts with initial point or line contact area can be performed using analytical formulas derived with rather broad assumptions. Some important issues related to contacts between non-conforming surfaces, including analytical expressions for contact deformations for some important cases, are addressed in Section 4.2.