How Fly Rod Guides Are Measured
Fly rods are certainly a strange animal. The tip top inside tube diameter are measured in fractions, snake guides are measured in a numeric system, stripping guides are measured in millimeters. No wonder there are questions about how to measure or what the measurements mean.
To start off with the most questions we get are about stripping guides. Stripping guides are measured between the frame holding the ring whether it is ceramic, carbides or agate. So a 12mm stripping guide measures 12mm between the frame and not the opening of the insert. The opening of the insert will vary depending on the type of ring insert used. The image below shows the D or diameter of a typical stripping guide.
There are typically three types of fly rod guides. An inserted guide which can be not only the stripping guide but also the running guides; snake guides and single foot guides.
Inserted guides again are measured from inside the frame. Snake guides and single foot guides are given a numeric indicator such as #2/0 through #6, #6 being the largest snake guide made. The chart below give the measurements of snake guides but they are not standardized throughout the industry. Some snake guides are taller than others and the openings (diameters) also vary by manufacturer.
A typical snake guide’s diameter is measured from the outside of the wire, the height is measured to the top of the guide and the length is the overall length of the guide feet.
We don’t really worry about the actual measurements of our snake or single foot guides we just make sure the smaller ones go towards the pointy end of the rod. Guide spacing is somewhat consistent but the guide size will vary with the rod’s line weight. That doesn’t mean that there is a standard chart for what size guide you have to use on your custom build just remember that the guide’s job is to keep the fly line near the rod during the cast. Too many guides do not improve performance and too few guides are not good either. Typically for a fly rod the number of guides will be the rod’s length in feet plus one. Therefore a 9’0″ rod will have 9 + 1 or 10 guides. The number of stripping guides is also relative to line weight. A trout rod requires only a single stripper whereas a higher line weight rod will require 2 stripping guides.
These are just some general guidelines to help you decide which guides you want on your custom build. And by the way this is where a good set of calipers will come in handy. I personally use calipers that show not only inches in decimals but also millimeters and fractions.