The trivial example is the rules about selling weapons directly, so as a
very simple example of this you could take:
https://www.brusselstimes.com/153970/wallonia-faces-new-chal...
But this is the one-component-is-the-weapon, with everything going in one direction version of such a rule. An F35 has 300,000 components from 19 countries, so you can imagine what a maze the agreements for that one are.
It's also not just about the weapons and the danger they pose. It's also about jobs. Know-how (both spreading and restricting know-how). And even the traditional "synergy" (you've designed helicopter blah, hence you make radio component so-and-so, so how about you manufacture NATO standard blah radios and antennas) and the occasional monopoly (it's kind of secret but there aren't many companies that can make the obvious alloy needed for the trust vectoring to name one obvious thing)
Our side is NATO, and we make weapons that are designed to push the global integrated worldview and human rights ("America and it's allies") that we espouse as an alliance. And this view permeates all weapons. For NATO guns, one, you'll never get ridiculous ammo stores (that would enable you to eliminate a population for example), we all work on these weapons together, design them together, and if you try to use your own ammo, everything will fail. Most NATO weapons are defensive. You aim a NATO weapon at a (small) target, it finds that target and either kills it or it disables itself and falls to the ground, essentially intact. Russian weapons are the total opposite: they're meant to kill and if they can't kill their target, they'll just kill whatever and whoever's nearby. Sometimes up to the point they kill the weapon's operators. They will fire "cheap ammo" and literally come with instructions on how to make it. They are meant to kill on a very large scale, without precision and they are most definitely not safe to use. This philosophical difference applies to everything from machine guns to nuclear weapons.