If a blank has a rating of say, 20-40lbs, what does that actually mean? Will it break at a load of 45lbs? Does mono vs braid have an effect? I’ve always been curious how or what criteria blank manufactures use to establish line rating.

Most are simply suggestions as to what lines the manufacturer feels would be most appropriate for a blank. If you are talking about those that are class rated for a line, those ratings represent a certain blank power.

Most blanks will break on a deadlift before the top end line rating would.

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These ratings date way back, probably to linen line days. A line's pound-test rating means little without specifying the type of line referred to: nylon monofilament, fluorocarbon monofilament, nylon braid, super-braid? Today rod blank manufacturers & retailers reveal little useful information about their products more than length and weight.

I believe it to be guide as to how much the power of the blank is intended for. Most of the ratings on rods and reels refer to monofilament line but that all goes out the window when you start using braided line. Those ratings can differ from one manufacturer to another. I look at it as a guide to the size fish I am going after.

I expect Tom Kirkman has the most expertise for answering the direct question about line rating.

I really don't use it for anything. But I would like to comment on the information one gets on blanks from the manufacturers, even knowing I may be opening a can of worms. I'll make just this one post.

The action ratings are subjective but not worthless. Within a maker's offerings their descriptions of moderate, moderate fast, fast, extra fast are all accurate in determining the relative speed of the blanks offered. You won't find a maker's fast being slower than his moderate fast. Similarly, the power ratings, while also subjective, are accurate with respect to each other for a maker's offerings. You won't find a maker;s medium power that is less powerful than his medium light, and it won't be more powerful than his medium heavy.

One number that they give that is objective and pretty accurate for all makers is the recommended lure weight. I find this a valuable number for the freshwater and inshore rods I build. It tells the best range of lures that will load the rod properly when casting. You can go above it, but will want to slow down your casting to be more of a lob. With lighter lures, the rod will work, but not as well since it doesn't store and release energy very efficiently.

I find that all the blanks rated for certain actions, (as in moderate, or fast, or extra fast) that I have tested for CCS action angle, regardless of brand, all fall into a small range of action angles. This is true for casting and spinning blanks. But with respect to this number, fly rods are a separate population which is also consistent for this characteristic. A fast action fly rod will not have the same action angle as a spin/cast.

Once a builder gains experience and expertise he will know that a specific brands' medium powers are a little more or less powerful than another specific brand. So while the info is not all subjective, it is usually consistent, and while the providing of objective data in addition to the subjective would be better than what we get now, what we get now is definitely useful .

Does a "moderate" action refer to "moderate" for a fiberglass blank, a composite blank, or any graphite blank - and how can I find out before I spend my money to buy a blank? That is, "moderate " compared HOW and to WHAT? Rod blank vendors prosper by selling cords of "medium" or "fast" or "slow" or "extra-fast" rod blanks to poorly informed rod builders and their customers.

Action is independent of rod material. Or, by definition, it should be.

A fast action bamboo rod will have the same action as a fast action graphite rod (within the scope of the relatively poor resolution).

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Fly fishers are a reasonable lot. A 5 weight fly rod should cast best with a 140 grain line [1st 30'] a 7 wt. with 185 grain [1st 30'] an 9 wt. line 240 grains, etc. - a considerably more helpful system than "medium weight spin rods cast medium weight lures on medium test lines best".