Chief Delphi - 10-32 or 10-24?

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Originally Posted by DampRobot (Post 1340562)

10-32. All the things others mentioned, plus you can tap them into thinner material and still get the required six threads of engagement.

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Originally Posted by magnets (Post 1341324)

10-32's!!!

Easier to tap (saves money with fewer broken taps), stronger, get a tapped hole in thinner material.

There is no magic universal number of threads to have in the tapped material, it depends on the diameter of the bolt and the relative strengths of the fastener and the material that is being tapped.

The general rule of thumb to ensure that the strength of the tapped hole is similar to that of the bolt you are threading into it is to have the thickness of the tapped material equal the diameter of the fastener when the materials are similar in strength. When the tapped material is not as strong as the bolt you are threading into it such as a steel bolt into aluminum you want the thickness of the material to be 2x the diameter of the bolt.

So using a 10-32 instead of a 10-24 does not mean that you can universally tap into thinner material. With either fastener if you are tapping into aluminum to accept a steel bolt you'll want the material to be 3/8" thick. So for a 10-32 you want 12 threads while using a 10-24 you would only need 9 threads to achieve similar strength of threads in the tapped material.

Head to your local hardware store and take a look at the different sized nuts and you'll find that the height of the nut gets larger as the size of the bolt does and you will find that a fine and coarse thread nut has the same height. If you have a store that also stocks aluminum and/or nylon fasteners you'll find that the height of the nut is the same for those made of steel, since they are intended to be used with bolts made of the same material.

That being said the Socket Head Cap Screws that many FRC teams use is way overkill for most applications, so tapping into material that is thinner than the rule of thumb suggests will work just fine.

Here is a good discussion of coarse vs fine and the benefits and drawbacks of each. http://www.katonet.com/article/coarsevsfine.html

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Coarse threads are more durable and have greater resistance to stripping and cross-threading.

The part I put in bold is exactly why I insisted that we standardize to 10-24 after my first season with my team, since for many of our students being on our FRC team is their first experience with assembling things with nuts and bolts. As mentioned above the bolts are usually overkill so the greater strength of the fine thread bolt is not necessary. Using nylock nuts or thread locking compound means that the fact that fine threads are less likely to loosen isn't necessary either.