How much does diameter change a dock line's working load?

No. Extreme Max calls its number a working load limit and Better Boat says working load; neither figure here is a breaking strength. Don't line either one up against a breaking-strength rating from another brand, because they describe different things. Either figure describes the rope alone, so it can't size a boat or vouch for your cleats and chocks. A lot. At 3/8 in, Extreme Max rates 550 lb and Better Boat’s two-packs claim 820 lb. At 1/2 in, their figures are 870 lb and 950 lb respectively. Extreme Max’s 5/8 in lines rate 1,600 lb. Its ratings apply at every length. Neither maker gives a measurement method, so the brand gap remains a claim. Only Extreme Max offers it.

Each Better Boat entry buys two black lines, while each Extreme Max BoatTector entry is one line in white and gold, so halve the Better Boat price before you compare. The eyes differ too: Better Boat describes a whipped eye (heat-treated on the thinner pair), and Extreme Max a spliced soft eye.

Neither is here. All ten are fixed-length double-braid nylon dock lines with the same size of eye, so construction won't separate them; diameter, length and whether you want one line or a pair will.