6 Side detection using hough transform

I have an Image consisting of different screws heads of different shape, some are circular, hexagonal and flat (rectangular) I need to detect 6 side shape using Hough Transform. I have applied line Hough transform but it detects the line segments. How can I use this information to decide the shape of figure

[Image Analyst]

Why do you need to use that technique? Also, you forgot to attach your image. click here