Fastenal is boring but profitable. It's been growing at about 15% a year just being a middleman for fasteners. How can they pull it off? Well, neither buyers nor sellers have a lot of market power. The buyers are generally dispersed, and they're not going to band together and demand better pricing on some bolts. And for sellers, they have the best distribution system by far - apparently it can be hard to ship fasteners, some of which are heavy or oddly-shaped.
Right now, I think the stock is cheap. Not as cheap as Apollo, Compton, or Banco Popular, I admit. But the growth story here isn't broken (Apollo's is dented, BPOP's is heavily dented, Compton hasn't been noticed yet), and the management team is good and aligned with minority holders' interests.
Note for socially responsible investors: the Domini Social Index holds Fastenal. Domini's site says that Fastenal provides excellent customer service, and has reasonable executive compensation. Of concern is that they don't make matching contributions to employees' 401ks - compensate your people well and you can reduce turnover, as Costco and Whole Foods do.