又叫补心或内外丝，用于将小口径管子连接于大口径管子内的管件。 水暖安装中常用的一种管件。补心又称内外螺纹管接头，用于直线管路变径处。一般立管变径必须采用大小头，支管可以采用补心连接，如水表变径处的连接。
bush ; bushing ; pipe lining
试映羊毛采用高纯石英制成，非常适用于进样口衬管。
Quartz Wool was made from high-purity quartz, extremely low in metallic oxide impurities.
在套管或衬管与周围的水泥环之间所形成的小间隙，这些间隙是由于在固井期间或固井之后温度或压力的变化所致。
A small gap that can form between the casing or liner and the surrounding cement sheath, most commonly formed by variations in temperature or pressure during or after the cementing process.
管腔纵切面：单层立方上皮衬于管腔内。一些立方细胞之间的边界相当清晰明显。
Simple cuboidal epithelium lining a tubule (longitudinal cut). Some of the cell boundaries between "blocks" or "cubes" here are quite distinct.
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