noun
screw thread; ridge of a screw
Refers to the helical ridge on a screw or bolt. Technical term used in mechanical contexts.
このボルトはねじ山がつぶれている。
The screw thread on this bolt is stripped.
ねじ山のピッチを測ってください。
Please measure the pitch of the screw thread.
ねじ is the general word for a screw or bolt, while ねじ山 specifically refers to the thread or ridge on it.
Compound of ねじ (screw) and 山 (mountain, peak), referring to the raised helical ridge of a screw.