| 摘要 |
The composite level consists of an I-shape aluminum frame having ribbed or working surfaces and a pair of one-piece plastic cover plates integrally formed with end plates secured to the frame. A plurality of measuring vials are supported by the frame and retained by the cover plates. The alignment between the plastic cover plates and the metal frame is provided by an indexing system that minimizes the deleterious effect of the shrinkage of the plastic material of the cover plates during the curing process on the fit between the cover plate and frame. The use of the plastic cover plates and the ribbed working surfaces of the aluminum frame eliminate the necessity of painting and milling the level.
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