Figure 11-5.-Ball bearings. A. Radial type; B. Thrust type. 4. 5. 6. 7. Self-aligning roller bearings with a spherical outer  raceway Self-aligning roller bearings with a spherical inner  raceway Ball thrust bearings Needle  roller  bearings Roller  bearing  assemblies  are  usually  easy  to disassemble  for  inspection,  cleaning,  and  replacement of parts. Ball bearings are assembled by the manu- facturer  and  are  installed,  or  replaced,  as  a  unit. Sometimes  maintenance  publications  refer  to  roller  and ball bearings as either trust or radial bearings. The difference between the two depends on the angle of intersection  between  the  direction  of  the  load  and  the plane of rotation of the bearing. Figure   11-5,   A,   shows   a   radial   ball   bearing assembly. The load shown is pressing outward along the radius of the shaft. Now suppose a strong thrust were to be exerted on the right end of the shaft in an effort to Figure 11-6.-Radial-thrust roller bearing. move it to the left. You would find that the radial bearing is not designed to support this axial thrust. Even putting a shoulder between the load and the inner race wouldn’t support it; instead, the bearings would pop out of their races. Supporting a thrust on the right end of the shaft would  require  the  thrust  bearing  arrangement  of  the braces  shown  in  figure  11-5,  B.  A  shoulder  under  the lower race and another between the load and the upper race would handle any axial load up to the design limit of the bearing. Sometimes  bearings  are  designed  to  support  both thrust and radial loads. This explains the use of the term “radial thrust” bearings. The tapered roller bearing in figure  11-6  is  an  example  of  a  radial-thrust  roller bearing. Antifriction bearings require smaller housings than other bearings of the same load capacity and can operate at higher speeds. SPRINGS Springs are elastic bodies (generally metal) that can be twisted, pulled, or stretched by some force. They can return to their original shape when the force is released. All  springs  used  in  naval  machinery  are  made  of metal—usually   steel—though   some   are   made   of phosphor bronze, brass, or other alloys. A part that is subject to constant spring thrust or pressure is said to be 11-4