求翻译：（3）由于轴与外壳材料因膨胀系数不同，会导致游隙值的缩小或增大。通常向心轴承选择最适宜的工作游隙值就是轴承游隙标准中所规定的基本组游隙值。基本组游隙值适用于一般条件，应该优先选用。对于在特殊条件下工作的向心轴承不能采用基本组游隙时，可选用辅助组游隙值。如深沟球轴承的第3、4、5组游隙值，适用于轴承与轴和外壳孔采用比正常配合更紧的过盈配合或轴承内圈与外圈工作温差较大的机械部件中。在轴中心与外壳孔中心线倾斜度较大，和为了增加其承受轴向负荷能力，提高轴承极限转速，以及降低轴承摩擦阻力等工况条件下，亦可采用第3、4、5组游隙值。对于要求旋转精密或限制轴向游动的轴，一般采用第2组游隙值（小游隙值）的轴承，必要时还给予一定的预加负荷“预紧”，以提高轴的刚性。是什么意思？

(3) for different coefficients of expansion due to the shaft and housing materials, can lead to reduce or increase the clearance values. Radial bearings usually choose the most appropriate operational clearance value is the bearing clearance standards stipulated in the basic set of clearance values. Basic Group clearance values of General conditions should be preferred. For radial spherical plain bearings working under special conditions when there is no basic clearance, the choice of secondary clearance value. Such as deep groove ball bearings, 3rd, 5 clearance values, apply to bearings and shafts and shell holes than normal suit more aggressive interference fit or bearing of large temperature difference between inner and outer rings in mechanical parts. Tilt axis Center and the shell hole center line is large, and to increase its axial load carrying capacity, improve bearing limit speed and reduces bearing friction resistance under the condition, may 3rd, 4, 5 group clearance values. Precision or limiting of axial walk which require rotation axis clearance values generally use the 2nd group (small clearance values) of the bearing, if necessary, giving certain preloading "preload" to improve rigidity of shaft.