tightening

Make sure the washer is firmly seated before tightening the pipe.

旋水管之前,检查一下洗衣机是否已牢牢地定在底座上了。

That membrane proceeds to wrap over the nerve fiber with machinelike precision, spiraling down to create the distinctive sausage shape, tightening itself over the fiber like a threaded nut.

这层隔膜就象机那样的精确包裹在神经纤维上，并旋转缠绕成特殊的香肠形状。就象螺母那样地包在神经纤维上。