Left vs right thread 1

[Loco_]

Hello all,
My first thread on this forum.
Could someone explain to me when the left-hand thread is used? Till yesterday, I thought that when a shaft or pulley is rotating clockwise, the right thread is used because it is the direction of tightening, and this will prevent the bolt from coming loose. I saw this on some designs like bicycle pedals; on the left one, the thread is left, and on the right pedal, the thread is right-hand. But when I was rebuilding a car turbocharger, I noticed that a compressor turns clockwise and has a left thread nut. It's the opposite of what I was thinking. I am confused now, and for some of my designs, I need to be 100 % sure when to use the left thread.
Thanks in advance. Matthew.

 

[Denial]

Thanks for the correction, Prometheus. It was more than fifty years ago, and I have never touched an oxy-torch since then. A good thing I haven't, since I remembered it totally wrongly.