Power wire question

this isn't for stereo aplication, but thought it was best to post it here.

If I have an 8 gauge wire that I need to add a fuse to it could I add this port fuse to it (taking in consideration that it will have an inch of 12 gauge wire on each side)

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basically I will have:

3 inches of 8 gauge wire this fuse holder (with 1 inch on each side with 12 gauge wire) 4 feet of 8 gauge wire to a relay with about an inch of 12 gauge wire on each side and then again 2 feet of 8 gauge wire to my power source..

will it affect power? since at a certain point it has 12 gauge wire, will that make my whole "setup" 12 gauge instead of 8?

all connections are solder


application called for 10-12 gauge wire, but since it was fairly the same price I bought 8 gauge