Wire size varies with factors such as water clarity, bait size, and the realistic expectations of local kingfish dimensions. No. 3-4 wire is common for leaders with No. 4-5 preferred for the stinger segments, which usually see the most teeth. In areas known for giant kings of 50-plus pounds (Key West, the northern Gulf, etc.), No. 5 leaders and No. 7 stinger segments are not uncommon. Go any lighter and you’re just gonna get your feelings hurt.