This is a front dropout spacer for a standard 100mm spaced bike fork. It's used during shipping to protect the fork from damage.
When you ship a complete bicycle, you generally remove the front wheel and install a dropout spacer in the fork. When shipping a frameset that hasn't been built up, you use dropout spacers in both front and rear dropouts. This model is for just the fork, and is spaced to fit most road/hybrid/cyclocross forks, plus all mountain fork that take standard QR axles.
The fit will be a bit of a snug fit on most forks. This is a *feature,* not a bug :)
More info here: http://pencerw.com/feed/2013/11/18/update-dropout-protector