Default Screw Size, 10-32 or 10-24?

[Michael]

Number 10 screws seem to be the transition point between using course threads (larger sizes) and fine threads (smaller sizes).

During my entire career spanning various industries including aerospace, semiconductor equipment and other hi-tech fields the standard practice was 10-32.  I never asked why, it just was.  I believe part of the reason is that this was the fastener sizes companies stocked.

Recently I see an uptick of 10-24 usage.  Curious.

What is your experience?  What industries have you see one or the other or both?

[Noah Burk]

During my time doing design in the automotive industry we stocked course thread screws so #10-24 was the norm. Since starting at Pipeline and working on projects that span more industries I noticed the same thing, #10-32 seemed to be the norm, but I never really questioned why. Its funny to me that for what ever reason that size dictates a fine thread even when the need for a fine thread isn't present. I've never ran into a supply issue with either but I haven't been in the industry very long. I haven't looking into the cost difference between course and fine threads with matching materials and lengths, but that could could also be a driver. Of course supply has an effect on the cost, but cost is the thing you see first hand. I will do some research and post another comment!

[Noah Burk]

I took a quick peak at a screw type I use frequently from McMaster-Carr, Socket Head Cap Screw with a material of 18-8SS and there isn't any major cost differences. 

Looking at lengths like 1" that have the same package quantity the difference is $1.56, which is a little more expensive but negligible when compared to the total cost of most projects.

[Mark]

I have always preferred the 10-32 variety. This might only be because I can get a #6 and a #8 with the same thread pitch so it seems more uniform. #10-24 just seems dirty. I do actually prefer to use fine threads on the larger sizes as well but those are not as common and add to assembly time.