Identify exact size/type of screw

[shmokes]

This is a long shot, but I went to Ace today and couldn't find the screws I need.  I have a a Logitech MOMO Force steering wheel.  I want to mount the pedals permanently to a piece of metal.  I planned to just remove the screws from the bottom that hold the pedal unit together, and get longer screws to go directly through the metal piece, and screw into the original holes on the pedal unit.  But I can't quite identify what type of screw it is.  I need the threading to be exact so that the pedal unit will accept the new screws.

Anyway, the closest I could come is a #4 machine screw, but when I eyeball the threading on the #4 screws at Ace it looks slightly different.  Either way, Ace doesn't have the proper lengths, but I've found a place online that has #4 machine screws in the lengths I need.  But I don't want to order a bunch of screws online only to find that they don't fit. 

Does anybody know screws well enough to identify this from a picture?  I've included pictures in inches and millimeters.

[massive88]

Screws are usually defined by four attributes:

1) The type of head, those look like panheads
2) The length, those look like 1/2"
3) The major diameter, thats the dimension from the edge of thread to edge of thread, perpendicular to length axis.  From attempting to scale from your picture, it seems to be around 0.1875" - you should verify this, but that would put it right at a #10 screw
4) The thread count, or how many threads per inch.  It looks like there are 12 in that half inch shot, so this number should be 24, which would help to confirm the #10 size, that is a typical thread count for #10s.

So, my best guess, is that you need #10-24 Panhead screws, 1/2" long.

#4 Screws have a major diameter of 0.11", and will typically have a thread count of 40.

[cadmium]

I'm not an expert by any stretch, but I think screw length is measured from below the head to the tip, so that looks like 1/2" machine screw of some kind.

If you have a Home Depot nearby they usually have a board with common size screw holes in it you can test for size.

[shmokes]

Screws are usually defined by four attributes:

1) The type of head, those look like panheads
2) The length, those look like 1/2"
3) The major diameter, thats the dimension from the edge of thread to edge of thread, perpendicular to length axis.  From attempting to scale from your picture, it seems to be around 0.1875" - you should verify this, but that would put it right at a #10 screw
4) The thread count, or how many threads per inch.  It looks like there are 12 in that half inch shot, so this number should be 24, which would help to confirm the #10 size, that is a typical thread count for #10s.

So, my best guess, is that you need #10-24 Panhead screws, 1/2" long.

#4 Screws have a major diameter of 0.11", and will typically have a thread count of 40.

So useful.  Thanks.  I didn't know what that second number was for (e.g., the 24 in #10-24).  I'll go back to Ace tomorrow and buy one and bring it home to see if it's a good fit.  If it is I'll probably still have to order online cos I need some uncommon sizes that I don't think Ace carries.  Or maybe they'll have my lengths.  maybe their selection of #10 screws will be better than the #4 selection. 

The strange thing, though, is that by physically comparing them today the closest match I could come to was a #4 screw.  #10 is a long ways from #4.

[massive88]

Its tough to tell from the picture what the major diameter of the screw is.  I was literally holding a ruler up to my screen to try and scale it out.  You are right though, a #10 is almost twice as thick as a #4

You can probably do a more accurate job measuring the major diameter yourself, especially if you have something more exact to measure it with, like calipers.

#4 screws usually wont come very long, just because they are so weak in bending, they aren't used in long applications (Bending strength is related to diameter^2).  There should be a better variety of lengths the bigger the screw diameter, since it should be roughly 4x as strong in bending.

[shmokes]

Damn . . . it's definitely a #4-24.  I got some bolt-sizing things.  They practically don't exist, and so far I haven't found anything in the sizes I need 1"-2 1/2"