Both have the same pitch diameter at the top of the hole of internal threads or end of the pipe on external threads, and both have the same thread lengths or depths.
在内螺纹的孔的顶端或者外螺纹的管的端部拥有相同的中径，而且拥有相同的螺纹长度和深度。
The external diameter of the middle part of each guiding expansion head is larger than that of the through pipe.
导向扩张头中部的外直径大于通管的外直径。
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