Good Screw Sizes fo General Use
 

Hello all,
I have to give in a list of consumables to one of our local sponsors as he would like to donate all of our screws, bolts, nuts, and wire. What general sizes of screws and bolts are best to stock up on for the upcoming season?

Thanks!

Re: Good Screw Sizes fo General Use
 

We heavily standardize on #10-32, and love it.

Vex has sort of standardized on #8-32, but has some #10 and 1/4 mixed in.

Re: Good Screw Sizes fo General Use
 

For nuts we like to use KEPS and Nyloc variety. KEPS have a built in star washer and are cheaper than Nyloc, but Nyloc gets the job done without the need for excessive torque or loctite

Re: Good Screw Sizes fo General Use
 

What we stock:

8-32
10-32
1/4-20

Socket head cap screws from 1/2" length up to 3" or so.
Also lots of nylon insert lock nuts and flat washers. Black oxide preferred over other materials.

Re: Good Screw Sizes fo General Use
 

10-24, 10-24 and 10-24. For lengths 1/2" to 1 1/2 or 2" is a good range. Make sure the nuts are nylocks.

10-24 is plenty strong enough and having 1 size means it is less likely that someone who doesn't know a lot about using fasteners will put a #10 nut on a #8 bolt. I recommend the coarse thread (-24) since they are harder to cross thread than fine thread (-32).

Note many of the COTS items do use 10-32 and 8-32 so a few of those in shorter lengths are not bad to have on hand, just store them separately and have them specifically labeled as to their uses.

#10 is nice in that you can use the same hole size for those and 3/16" rivets. So you can bolt things together until you are finalized and then switch to rivets when you know that you are using that configuration or it isn't likely that you will need to remove that item for service.

So ask for some high strength 3/16" rivets too.

1/4" is overkill for most applications and #8 are strong enough for many applications but having one size fits all makes for less items to stock and less confusion.

Re: Good Screw Sizes fo General Use
 

We use mainly #10-32 (Black oxide) and some #1/4-20, but the #1/4-20's are mainly used for high stress/abuse parts. For nuts we mainly use nylon lock nuts and standard hex nuts.

Re: Good Screw Sizes fo General Use
 

5/32" rivets; #8-32, #10-32, and 1/4-20 screws.

The 5/32" rivets are most common individual hardware, followed by #8-32 and #10-32 screws for general purpose mechanisms. 1/4-20 screws are pretty much exclusively used for tube axles (dead axle shaft+standoff combo) or high-loading parts.

I try to avoid #10-24 and #6-32 like the plague as these are the most commonly broken tap sizes due to their ratio of pitch to shank diameter (look at a #6-32 tap wrong and it breaks), and #10-32 is WAY more common for COTS stuff.

Re: Good Screw Sizes fo General Use
 

We use #10-32 and 1/4''-20 bolts (socket head preferable, hex head for 1/4''-20 also OK, phillips head is a no-no since they're basically designed to strip) for structural bolts. Trying to move more towards the former as the latter really is overkill for most stuff in FRC. Nylock nuts are standard.

After years of frustration, mismatched nuts, and accidental crossthreading, we will no longer purchase #10-24 on either team I mentor.

Re: Good Screw Sizes fo General Use
 

Make sure you get the nylon/teflon nuts that self-lock (Nylock Nuts) so that you don;t have to loctite screws. They come in thick and thin profiles for different applications as well. They are so easy to use and never have I seen one vibrate loose if properly tightened.

Re: Good Screw Sizes fo General Use
 

We use mostly 10-32 on our robot. 1/4"-20 is good for some high-load applications. Dead axle screws.
Nylock nuts are really nice, but get some thin ones too. They come in heights of 9/32" normally and 1/8" (4/32") for the thin ones IIRC for 10-32 screws.

We use a lot of 1/8" rivets. Vex uses 5/32" for the versachassis. 3/16" rivets are interchangeable with 10-32 screws in terms of hole size.

Re: Good Screw Sizes fo General Use
 

We use almost exclusively #10-32 hardware and 3/16 rivets so we only have to drill one hole everywhere. #8-32 screws and 5/32nd rivets are used to interface with weird Vex stuff sometimes.

Socket head cap screws basically every time.

Re: Good Screw Sizes fo General Use
 

Whatever the job requires. #10-24 is generally the first bolt we reach for (if something can't be riveted). We'll use 10-32 if we need more thread engagement, but they just take to long to screw in and out. Our one general rule is absolutely no metric unless we're forced to.

Re: Good Screw Sizes fo General Use
 

The rule of thumb for thread engagement is in hard materials like steel you want 1x the bolt diameter and for soft materials like aluminum you want 2x the bolt diameter. That does not change whether you are using coarse or fine threads. If you look at standard steel nuts you'll find that their height is 1x the bolt diameter. So going to 10-32 to get more thread engagement isn't really gaining you anything in fact if it is in Aluminum you are more likely to strip the threads out of the item that you have tapped.

The only real advantages that find thread have are the the bolt itself is slightly stronger and that it is slightly less prone to loosening from vibration.

http://www.bestbolt.com/white_papers/white_paper_08.pdf

Re: Good Screw Sizes fo General Use
 

We're usually not tapping into aluminum when 10-32 were used. One way we used the 10-32 last year was in our chain tensioning system. We fed the 10-32 bolt into a helicoil. If we're tapping into aluminum, it usually is UNC. By far, 10-24 is the most common bolt we use. A recent exception was in an experimental drivetrain, because the only #10 SHCS we had was #10-32, and we needed that size and head type.

Re: Good Screw Sizes fo General Use
 

#8-32 screws are nice because you can easily cut them to size if needed.

We stock 1/4", #10, #8, #6, and #4. Socket cap is the only way to go.

I would also request some #10-32 rivet nuts (ribbed) and some #8-32 threaded inserts like this. The inserts are useful for bumper building.

Re: Good Screw Sizes fo General Use
 

We've standardized to 10-32 as much as possible. Generally SHCS style. Rivnuts, t-nuts, and nylok nuts. It has made life suck a whole lot less to standardize everything.

Re: Good Screw Sizes fo General Use
 

Last year, almost everything we had was 10-32, allen-drive cap screws and nylon nuts (all steel). This worked out quite well for us; we might change to a different size or two this year (I'm mentoring programming this year, so not on top of the discussion), but we'll definitely have a small set of sizes for anything that we're building. When you do pick a standard size or sizes, STOCK UP ON TOOLS IN THOSE SIZE(S)! You'll never seem to have enough, since (for 10-32) everyone wants the 5/32" Allen and the 5/16" hex wrench at the same time.

Re: Good Screw Sizes fo General Use
 

What's the advantage of using socket head over button head?

Re: Good Screw Sizes fo General Use
 

Socket head typically has a deeper hex, so it's harder to strip out.

I like 10-32's over 10-24's because it's harder to break the 10-32 tap. As a rule of thumb, I try to get more than 6 threads of engagement in a tapped hole in aluminum. With a 10-32, that works out to 6/32 = 0.1875", but a 10-24 requires 6/24 = 0.250".

Once you've used both for a while, it becomes easy to identify the different threads on bolts, and you can check to see if your nut threads easily on a known bolt.

We've used 1/4-20's as axles for flywheel shooters and pivots for catapult shooters, as well as gearbox mounts.

3/8-16 or 3/8-24 is our favorite for dead axles.

Re: Good Screw Sizes fo General Use
 

You must not have "determined" kids that will get that 10-24 nut on the 10-32 bolt. Yeah sure, it'll go on...with enough torque.

Re: Good Screw Sizes fo General Use
 

Quoting for truth. As mentioned earlier in the thread, our solution to this problem is to just not buy 10-24 anymore, which removes the potential for the error in the first place. On a team as large as 449, it's just not worth the hassle for the few places where it's nice to have coarser thread.

Re: Good Screw Sizes fo General Use
 

Biggest advantage is the deeper hex, but you can also turn it with pliers if you're desperate which is nice. Also lends itself to counterboring.

Re: Good Screw Sizes fo General Use
 

Same. We actually cleaned out our old hardware organizer as we make room for these sizes in differing lengths and the accompanying washers, lock washers, nylock nuts, nuts, and acorn nuts.

Re: Good Screw Sizes fo General Use
 

Not only does the socket head have a deeper tool engagement the tool size is usually larger for the socket head making it less likely to damage the tool or bolt. The button head is also weaker than the socket head.

Because the fine threads are not as deep (the reason it is harder to break the tap) you need more of them to have the same strength. If you look at standard nuts you'll find that their height is equal to the diameter of the bolt they work with regardless of the pitch. In other words 4.5 10-24 threads will give you the same or greater strength as 6 fine threads. The fine thread bolt will be stronger but in both cases the threads will pull out well before the bolt fails since you need 2x bolt diameter in aluminum to make the tapped threads roughly equal to the bolt strength.

It is true that once you've worked with threaded fasteners for a while it does become second nature for many people. The problem is that there are a new group of people added every year many of whom are experiencing using threaded fasteners for the first time. Because there are many new people every year that is another reason to not use fine thread fasteners because they are mush easier to cross thread.

Re: Good Screw Sizes fo General Use
 

In the case of wire - stranded black and red. DO NOT USE White (correct Stratis :D - a la 2013 FRC 4607 @ North Star)...

Be sure to check the manual and the proper usage.

We try to keep plenty of 10, 12, 14, 16awg Red and Black on hand.

Care to chime in 4607 captain?

Re: Good Screw Sizes fo General Use
 

Another great suggestion for helping to avoid stripped Allen screws is to ONLY use high-torque Allen keys (from Wera).

I've used these since I was in college, and even for small sizes like 3/32" or 5/64" I've yet to strip one of these Allen keys. I've also been able to use these to remove "stripped" screws that regular Allen keys couldn't get out. They aren't much more expensive than regular Allen keys, so it's basically a no brainier.

Re: Good Screw Sizes fo General Use
 

Once you make the switch to hex head machine screws, you'll need to get some real hex keys.

We have a couple sets of the Bondhus HTX10/S T handle hex key sets, and they're great. If you're buying something like this, make sure that the metal of the key shaft goes all the way into the T handle. There are cheaper sets than the Bondhus that just have the hex key set into a plastic handle, which won't hold up.

$33 each on Amazon.

Re: Good Screw Sizes fo General Use
 

Thank you guys so much. We are going to use 8-32, 10-32, and 1/4-20 with nylocks (Keps just don't appeal to me...). We have a sponsor that will buy them for us for free off of Grainger.

By the way, I was looking on Grainger's website for wire too, I don't get teh difference between the different types of wire. What type of wire is best for our applications (I need to get this order in by Sunday and my coach doesn't know too much about materials as organization...)

LINK to GRAINGER Website

Re: Good Screw Sizes fo General Use
 

If you're building a house (no motion except in the occasional earthquake), go solid-core with THN insulation. If you're building a robot or a car (something that moves), go stranded, especially for anything above about 20 GA, and a more flexible insulation. If you want to buy local (vice online), go to the local auto parts shop, not the home improvement warehouse. All of their stuff is also for 12V, great for robots. Buying the red/black "zipcord" pairs really helps layout as well. Though honestly, for 6GA (battery to main breaker to PDB) you can probably do just as well buying a nice pair of HD jumper cables at the auto shop and cutting them up as trying to find the wire. One thing to watch when buying auto electrical though -- be sure you don't buy stuff that depends on a chassis ground -- this is specifically illegal for FRC, at least in recent years.