Is the thread direction in this diagram left-handed or right-handed?
Thread Content
The thread below has a lower left side and a higher right side; it is a right-hand thread. The thread on top has a higher left side and a lower right side – can it be considered a left-hand thread? If these two threads can be screwed together, shouldn’t they both be left-handed or both be right-handed?
Don’t overthink it; just take a set of bolts and nuts and have a look, and you’ll understand.