There's a lot more happening behind the scenes at McMaster-Carr than they let on. For example: this, in which I (signed in with my personal account) search for an item and get discreetly notified that my employer also bought some recently. How do they know where I work? I never configured such a thing. Their spartan and deceptively simple interface reveals no such options.
Granted, it wouldn't be hard to figure out. But I don't know of any other online shopping site that behaves this way. Pretty interesting.