Power lead to extra blade fuse in main fuse box

[bufpilot]

I need to tap a 10 gauge wire for a subwoofer into the main fuse box. I was planning on using the spare 15 amp blade fuse, but I can't figure out how to connect the two. The main fuse box appears to be a solid plastic piece; so, how does one connect a 10 gauge wire to it? Is there some interface that plugs into the place where the 15 amp blade fuse is now that I can attach the 10 ga wire to and then use the 15 amp fuse to protect that? Thanks for the help!