It’s not exactly a hot take on the internet that standard (SAE) is worse than metric, but working in environments where both types of hardware are being used is just the worst. Especially if something that was originally a metric piece of hardware, like a simple metal screw has been replaced by an SAE one. Sometimes at least the hole it goes into has been properly drilled and threaded, but other times (especially if the material it’s going into is aluminum) some Bubba will get 'er done by simply gorilla strengthing an SAE screw into metric threading. I sometimes discover this when my proper metric wrench or Allen key doesn’t quite fit correctly. I don’t carry SAE tools, so I have to go find somebody with a 1/27th or 6/18th or 420/69 or whatever stupid sized tool. Because at least with metric there’s no memorizing fractions for screw sizes so I can just look at a thing and think “eh looks about 6mm”. And what’s worse is the chances of stripping a screw go up about 100x in mixed environments because when people just mix and match, it’s much more likely for somebody not to notice their tool isn’t properly seating into hardware until they put their body weight into it and then it becomes my problem trying to fish out a stripped screw that requires me to remove 5000 panels to get good access to said mangled screw.
Anyway, how’s everyone else doing?
Sometimes a screw is just a screw. There are reasons beyond what you care about locally for an item on a large assembly. It could be physics related, it could be a miss calculation. It could be political or a payback engineer.
I’m not talking about the engineering side, I’m talking about an environment where some systems are metric and some are SAE, usually based on if they are US or European designed. In these environments, technicians who are sometimes not terribly well trained, who are doing daily work, will mix and match the wrong screws into the wrong systems.
It may just be “a” screw, but as I said it leads to these same people accidentally stripping them, which makes certain parts inaccessible until the stripped screw is removed. Which is a headache on top of whatever the actual headache reason is that I’m removing the screw in the first place. It’s extra yak shaving.
Well, you assume we don’t have that problem in engineering. If I want a prototype I can ask my local shop to make it, but I have to use imperial screws. For production we only use metric now. Anyone not using metric is just dumb or have not needed to change. All big machines in US shops have a high probability to be optimized for imperial units while mass production in China is usually metric.
In my line of work, sometimes we keep imperial screws for many reasons. For example, to prevent easy access, or to required a tool that we can provide because we want the acknowledgement that access gas been required. But yeah, the problem is definitely not just user side. You can thread an M6 into a 1/4-20 hole a few rotations before you realized you’re screwed.
Huh? What?
I’m working on finished systems designed entirely in metric, only designed with metric hardware. Installed with that metric hardware. The only way SAE hardware finds its way inside is when US technicians, who work for customers and not for my company ram it in there. Engineers are not consulted when they do this.
We just use metric security screws for most applications. Everything is supposed to be physically accessible by technicians who are theoretically qualified. Sometimes though they just aren’t.