The Fan of Hammers is another creation by Spencer. He gets the idea from watching a show about building things. One worker is asked if he prefers a nail gun or a hammer, and he responds that he is a fan of hammers, giving Spencer the idea to literally build a fan of hammers.
When Spencer is presenting his sculpture on the webshow, it has a malfunction, and one of the hammers flies off and almost hits Carly in the head, and is still there now. This happens in iWanna Stay With Spencer. The incident is again referenced in iChristmas.
In some episodes you can see the hammer that flew into the wall in the iCarly studio. In iSell Penny-Tees, the iCarly trio sells the Fan of Hammers, along with some other things that appeared on iCarly.