Not really, but they'd certainly make it easier. However, high precision CNC machines are useful in a wide range of high-tech applications, and keeping Iran po

Not really, but they'd certainly make it easier. However, high precision CNC machines are useful in a wide range of high-tech applications, and keeping Iran poorer makes the rate at which they can gain power slower. Harder to make smaller or more powerful jet engines, harder to make centrifuges for nuclear enrichment, harder to make more advanced computing fabs - and so on. If you can make it more expensive for Iran to advance to a particular level, then your investment in your own technologies puts you further ahead when they get there. If you get to cheap anti-ICBM defences first, then the threat of nukes is somewhat neutered, for instance. If you get to jet engines small enough for high performance combat drones first, then the threat of whatever airforce Iran can muster matters less. And so on. I would imagine that the reasoning behind such embargoes covers more grounds than just whether you can stop someone getting nukes or the like ever and has more to do with balance of power in general.