| 摘要 |
A caster assembly has a stem and ball bearing retainer made of a single homogeneous unit of reinforced plastic, a horn made of a single piece of reinforced plastic, a bottom bearing retainer made of a single piece of reinforced plastic, an upper set of ball bearings between the horn and the upper retainer, a lower set of ball bearings between the horn and the bottom retainer, with the bottom retainer being ultrasonically welded to the unitary stem and retainer.
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