Mounting Holes Figure 2-10A
illustrates typical mounting hole arrangements. From an engineering standpoint, the ideal means of mounting is by bolts passing completely through the bearing ring and the mounting structure. For cyclically loaded applications, it is necessary to have relatively long fasteners. Long fasteners retain a higher percentage of their original prestress after the seating of the threads and the other surfaces in the joint. Active fastener length should be a minimum of 4 times the fastener diameter. The use of through bolts makes it relatively easy to obtain this minimum ratio. Hex head bolts and hex nuts with hardened flat washers under each permit the use of generous clearance holes in both bearing ring and mounting structure, while still providing substantial load bearing area under the washers
.
Counterbored holes, are occasionally necessary to avoid interference with other components. In this case, the load bearing area under the heads is reduced and the allowable clearance in the mounting holes may be reduced, requiring somewhat more precise hole locations.

Tapped holes require the most precise hole locations because the total location tolerance in both mating holes must be accommodated by the clearance in the through hole.

Unless the mounting structure is exceptionally thick, ordinary tapped holes often result in unacceptably short fasteners. Far-side tapped holes, Figure 2-10C, provide for increased active fastener length and are recommended when through holes cannot be used.

Figures 2-10B through 2-10E illustrate the variation in active fastener length in various mounting arrangements. If a machine is equipped with a built-up deck structure, it is advantageous to bring the fasteners through the structure to maximize their length.

Figure 2-10E shows a method of increasing active fastener length often used as a field repair to eliminate loosening problems caused by inadequate fastener length.