When selecting a fit, first consider the type of load the ferrule will be subjected to. Usually there are three types of load bearing conditions for ferrules: 1 fixed load The resultant radial load acting on the ring is borne by the local area of the ring raceway and transmitted to the opposite area of the shaft or bearing seat. This load is called a fixed load. The characteristic of a fixed load is that the resultant radial load vector is relatively stationary to the ferrule. Neither the ferrule nor the resultant radial load rotates or they rotate at the same speed and are considered fixed loads. Ferrules that bear fixed loads can use a looser fit. 2 Rotating load The resultant radial load acting on the ring rotates along the circumferential direction of the raceway and is borne by each part in turn. This load is called a rotational load. The characteristic of rotating load is that the resultant radial load vector rotates relative to the ferrule. There are three situations of rotating load: (1) The load direction is fixed and the ferrule rotates; (2) The load vector rotates and the ferrule is stationary; (3) The load vector and the ferrule rotate at different speeds. 3 Swing loads and uncertain loads Sometimes the direction and size of the load cannot be determined accurately. For example, in high-speed rotating machinery, in addition to the fixed-direction load of the rotor weight, there is also a rotating load caused by an unbalanced mass. If this rotating load is larger than the fixed load, If the rotating load is much smaller than the fixed load, the resulting load will be a swing load. Regardless of rotating load or swing load, its magnitude and direction are constantly changing. Under variable working conditions, the load on some ferrules may be rotating loads, fixed loads, or swing loads. This type of load is called an indefinite load. Swing loads and uncertain loads should be treated the same as rotational loads in terms of fit. Too loose fit will cause damage to the mating surface. The ferrule and shaft or seat hole that rotate relative to the load direction should choose transition fit or interference fit. The interference size is based on the principle that when the bearing is working under load, the ring will not “creep” on the mating surface on the shaft or in the seat hole. When the load is very light, or the ferrule occasionally rotates at low speed under heavy load, a transition fit can be used. At this time, the shaft surface should have higher hardness and smaller surface roughness. For heavy load situations, the fit should usually be tighter than for light load and normal load situations. The heavier the load, the greater the fit interference should be.  

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