[gomerpyle]

When i go to the store , you see #6,#8,etc. also M6,M5, 1/4" etc.. Is there some conversion factor between them?

 

[Bob Mariani]

not exactly. the threads on the M6 are different then the ones for the English equivalent. A M4 is almost the same as a 8/32" but you cannot use one in place of the other.

 

[Mr Chips]

You can't really convert for thread pitch, but you can for diameter. A #10 wood or sheetmetal screw is approx the same as a 3/16 threaded screw (aka 10-24 or 10-32 depending on thread pitch). A number 5 wood screw is about 1/8", which is close to a metric M4 diameter. it can be confusing for sure....