discrete signals - How to count the number of threads in a bolt or nut using image processing?

How can I count the number of threads in a Nut with image processing?

I know that I need to find the place of threads and count them. Ok, But how can I find the place of threads?

This is a sample image:

Update As I know I need to do these steps:

1. Making image ready. For example az @A_A sayed, with Thresholding


2. Remove noise and just keep threads in the image


3. Count threads. maybe using signal processing

Level 1 is solved. What should I do for 2 and 3?

For example this is what I did for a bolt. I got a sample of a vertical line in the middle of the nut then plotted the data. But I don't know how to remove additional parts and count up and downs.

Thanks