Metric vs SAE hardware

We are a new team, so we can fully commit to one standard. Which one should we go with?

10-32 and 8-32 nuts and bolts are what we use. they seem to be very common in FRC

Since your location says CA, I’m assuming you will be building everything with materials that come in SI unit sizes. Most American teams additionally will have SAE hardware (if you need anything in the pits or whatever) and chances are you will see mostly SAE standards in the things you use (some FRC components are metric, but very few). I’d say SAE as your main system, though 271 usually keeps a very small box of metric stuff laying around in case we really need it. It’ll be more readily available, probably cheaper, and more compatible with everything else you might use, including VexPro and AndyMark products (who use SAE hardware on most everything).

Many of the parts you can buy from FRC Vendors, such as VEXPro and Andymark, sell most if not all of the parts in Standard units (inch). I would recommend going with this unit of measure.

Though it is likely most of your students will be using metric when they get into the work place (even in the America).

SAE is really handy because hardware stores stock it.
However, if you are able to order everything online, metric is generally cheaper for screws, bearings, etc.
So if you have the money to order everything and have enough machine tools to avoid AndyMark and Vex, go to metric.
If you have fewer than the maximum available resources and want to use Vex and Andymark parts, go SAE. Most likely SAE is better for you, especially if you live in SF.

Depends on how old your mentors are. I’m in my 50s, I love the old fashioned stuff.

If you dare to mix hardware, be VERY sure to label metric and sae hardware/tools differently. Like opposite sides of the room. Paint metric tools blue and SAE red or something.

Hex keys are almost cross-compatible, but can strip bolts. Same for wrenches (though those usually are easy to tell what size they are). Nuts are not compatible but somebody will try… see troubles with swapping nuts on main breaker and old PDB lugs. You generally had to trash the whole PDB when that happened. (not sure if the new one is different?)

McMaster sells metric screws with a blue coating. On the rare occasion you have to use metric, go blue.
We paint our metric allen keys red, and imperial keys yellow.

Agreed. Too bad that FRC/VEX/AM suppliers went SAE… So yes, you will be purchasing double the drivers/wrenches/etc. However, the positive side it is a great lesson on the power of a base 10 system!

I’m going throw a completley biased opinion in and say Metric.

We’ve been standardised on metric out of neceesity, but even then we’ve never had great dificulty with intrerfacing with AM/VEX etc. It’s true you need a second set of tools for many things, but I’ve found that more than enough socket, spanner and allen key sets often come with both Metric and SAE sizes anyway.

Don’t stress too much about mixing bolts, in fact, stripping out a screw head can be a very good leason in using the right tool - not just the one that fits! That being said, you don’t want that to happen at a competition!

In addition to standardizing on a measurement system, I would also advise standardizing on a thread pitch for each size. A couple of years ago, we tossed out almost all of our 10-24 hardware. We’re using 10-32, because of how much AndyMark makes use of this thread, but coarse threads for other sizes, which are certainly easier to get locally.

Many, many American companies use SAE / Imperial units and parts. I wouldn’t use the industry as a reason to make a decision one way or another - a well rounded engineer will have to learn both systems in either case.

In FRC, just because of all the COTS parts using SAE hardware and the overwhelming majority of teams using SAE hardware to build their robots, I see no reason to go Metric for hardware at all. For nuts and bolts, it’s about the same price, and you will need some SAE hardware on your robot anyway, so if you go metric for the rest of your hardware all you end up doing is creating unnecessary confusion and chances for error.

Save yourself a bunch of time and standardize on 10-32. You’ll need the occasional 8-32, 1/4-20, or 4-40 bolt, but you can almost exclusively use 10-32 hardware and really streamline things. Makes it easier to find bolts and tools, replacements, etc. without having to size anything.

For bearings, Metric bearings are much cheaper and more available, but FRC standardizes on SAE for bearings as well, so it’s probably just easier to go with that. Especially considering a lot of FRC bearings are proprietary (hex / ThunderHex)

Just don’t keep M8 bolts & 1/4 bolts in the same place. :ahh: Supply houses & hardware stores in the states still have a better supply of SAE than metric. Especially for things like taps & drill bits.

Our local Ace Hardware store is the go to place for nuts and bolts and screws…and they have about ten times as much space devoted to “SAE” hardware as they do metric hardware.

The older Power Distribution Board for the cRIO used metric M6 bolts for the battery input.

Not to be confused with 10-28 fine thread SAE which is very close.

Personally robots should be like so many American cars:
Totally unable to decide what should be SAE and what should be metric

Gotta keep those tool and die makers in business somehow.

Seriously: rivets just get the hole close.

I once pulled down a pan on an Oldsmobile transmission and inside it was stamped Ford.
At some point I guess you use what you got.

Mostly, the stuff that was already in production remained SAE, and the new stuff was metric. This started about the mid 1970s. Some of the old designs were used for several decades. You can still buy a new Chevy 350 engine (made in Mexico now) which looks and mostly interchanges with the 265 engine introduced in 1955.

“The game is played on a 27 by 54 foot playing field…”

That’s been part of the game description script for a looooong time now, and should be all the advice you need on which system to use.

I always described it as “We’re a Canadian team… we’re bilingual. We’re officially metric, but we speak Imperial because that’s what most of our friends speak.”


Kinda fond of furlongs per fortnight, eh?

Sorry, I had to,
(still trying to deal with a Farad implemented is the size of an Australian beer can, but femptoFarads are what a Si engineer needs to cope with)