Which type of screw or bolt do you think is generally best for building the mechanical components of robots? (I’d say Allen bolts, because they don’t strip.)
Torx hands down.
Jeep owners would not agree.
Allen (hex) button heads and flat heads, 10-32.
The kind you use for everything (really, if one tool can be used on any fastener on the robot every repair would be a lot quicker).
The kind that is most appropriate. I know how lame of an answer that is, but it’s not like they make so many different fasteners just for fun. They all have their special uses. That said, 10-32 socket cap bolts are pretty versatile and nice.
Hex head bolts are also nice, as are combination heads.
We standardized on the socket head cap hex screws. We have both socket and button but prefer button due to the lower profile. We carry mostly #6 thru 1/4-20 Very rarely we go over that. Usually coarse threads but #10 we standardized on 10-32 due to the amount of COTs and heritage parts that we have that used for it.
Team 228 primarily uses #10/32 socket cap head, #8/32 button head (VEX hardware), or a variety of rivets (mostly 1/8" and 5/32").
Supply and cost issues factor into this as well. If you’re in the market for relatively inexpensive screws, and located in Canada, Robertson parts and tools are easy to find (in wood and machine screws). If you’re not, you’re stuck with the thoroughly inferior Phillips.1
If you’re willing to spend a bit more, there are always Allen socket head cap screws. If you’ve got lots of money, you can even get Torx or Torx Plus cap screws. (Or maybe Posidriv, if you don’t mind confusion.)
Neither can ergonomics be ignored. Allen and Torx (all varieties) need only 60° of clear space to rotate the tool (and you can get ball-end drivers for more flexibility in driver angle). Robertson and Phillips need 90° of rotation and perpendicular engagement. Slots need 180°.
Then again, only Robertson drivers are tapered so that the screw can be held without magnetic tips (e.g. on some Phillips tools) or flexible rings (on some Allen and Torx tools).
Speaking of tips, I swear Phillips exists as part of a shadowy conspiracy to sell screwdrivers. Have you ever noticed that they’re the only screwdrivers that actually wear out in normal use? Whose bright idea was that?
The material surely matters. You wouldn’t usually want an aluminum Allen socket, because it would tend to strip more easily than the common hardened alloy steel fasteners. Robertson tends to be the most resistant to stripping—even in materials like brass—because of the deep, precise engagement and more acute angles. (But avoid the combination Robertson-slot heads like the plague. They are frequently malformed and strip easily.)
As for thread size, standardize when possible (and combine that with drive standardization). The real questions are metric vs. unified national and fine vs. coarse.
It turns out that it’s easier to find coarse threads in metric, so if you go that route, the choice is pretty much made for you. If you use UN threads, the fine (UNF) and coarse (UNC) ones are both relatively common.
Some teams, like the TechnoKats, have apparently gotten with the metric program and standardized on M5 as the most common fastener. (They just happen to be almost identical to a #10-32 UNC, which is convenient.) Most teams rely upon suppliers who don’t stock metric hardware, and can’t afford to invest in inventory of their own—so they use various bolts sold in Imperial units.
And by the way, check out aluminum pop rivets. They’re better than screws in a lot of cases—and considerably lighter.
1 Like the rest of this post, this is something of a generalization. You can find Robertson stuff in the U.S. if you look hard enough, or pay enough money.
1/4-20 is the way to go for our team. It’s pretty much the standard for everything, with only a few 10-32 exceptions, and even fewer 8-32’s. Personally I always like to have a 7/16" hex head, as we have dozens of 7/16" wrenches for standardization purposes. We also use allen heads, as we have a 3/16" standardized allen wrench as well. Torx really has no big advantage in the grand scheme of things other than impossible to find a driver for, so we just don’t use it.
The biggest thing I would say is to standardize. Pick a system and go with it.
Oh and whatever you do, whenever possible USE LOCK-NUTS!
TORX allows more torque than allen… I have stripped allen keys before, I have yet to strip anything TORX…
I can’t recall the last time I stripped a screw using 10-24 the Official Thread of every team I am associated with.
Seriously. We have a bin with about $500 worth of every combination of 10-24 screw and length and nut and washer…
We have established a hierarchy of uses:
Socket Cap, Button Head, Flat Head
Nyloc, Low Profile Nyloc, Nut with Captured Star Washer, Standard Nut, Cinch Nut, Tapped Hole
Washer on both ends, Fender washer if you need more distributed load,
Lock Washer if no Nyloc or Star Washer.
We have purchased a bunch of driver and wrenches and drill bits for this size screw.
We almost never need other tools to work on the robot.
It is a huge help to a team to standardize.
Joe J.
Philips screws were actually designed to cam out at high torque, because machines way back then couldn’t tell themselves “might break stuff if I continue, must stop”. 
I also personally hate 6 and 8 button head hex socket screws, because they’re so prone to stripping.
The type of screw doesn’t matter as much as the quality of the screw.
my team buys custom “security” bolts with the bat signal on the head never had one strip yet 
Certain types of screw drives/heads are more appropriate depending on application, and some are more prone to stripping than others are, regardless of quality.
I was going to suggest Robertson as well, but decided not to since I have never had the privilege to use them myself. All that I know is that after using Phillips for my entire life, I was thoroughly jealous when I first read a description of Robertson screws. Ford liked them to, he considered using them on his production lines to improve efficiency but couldn’t due to their limited availability in the US.
You wouldn’t be referring to clutch head bolts, would you?
I completely agree. But you can’t forget that a screw or bolt of poor quality is more likely to strip out than a screw of good quality. Basically, the universal rule of “you get what you pay for” applies here. I would much rather spend a couple more bucks on a box of USA made alloy steel or grade 8 bolts than a box of no-name junk made from unhardened steel.
At Team 3489 we need to keep this bolt chart handy:
