This is a protractor that can measure internal angles and requires four sets of M4 × 12 screws, M4 nuts, and washers for assembly.

这是一个量角器，可以测量内角，需要四套M4×12螺钉、M4螺母和垫圈进行组装。

我稍微改变了量角器的锁定部分，使螺钉更牢固地固定。

I slightly changed the locking part of the protractor to make the screws more securely fastened.