Regardless of reel type, the spool does more than just hold the fly line and backing; it forms an integral part of the reel. Most modern spools used for larger fish are machined from a single piece of aluminum. That may seem inconsequential, but the spools of smaller freshwater reels often get pieced together from multiple parts, and that's the last thing you want for salt water. Also, the runs of larger and faster saltwater fish can pack backing very tightly onto the spool.
Spools made from a single machined piece of material (usually aluminum) better handle the pressures that this tight packing can exert. Spools differ widely in how they can be removed and changed. By changing a spool, the angler can adjust his tackle to the fishing situation as needed; rather than strip off a hundred feet of fly line, you simply change spools. Also, some manufacturers make configurable reels that can adapt to a wide variety of line classes with a simple change of spools. Some reels have a button that releases the spool; others snap into place or have a screw that must be removed first. The mode for removal remains trivial as long as the method is quick, easy and secure, and does not compromise the fit of the spool onto the frame. Though few take much time to compare spool dimensions, the combined width and depth determine the volume of a reel, or how much line and backing the reel can hold.
The typical spool width runs approximately half of the spool's depth, a ratio that reduces a fly line's tendency to tangle. With larger widths, line builds up in a small hill on the spool (called caking), causing tangles as the line slips off of the hills. Smaller widths don't offer enough volume to satisfy most consumers. Arbor diameter determines the depth of the spool, and recently large-arbor reels have become quite popular. As we all learned in school, the larger the diameter of a circle the greater the distance around the circumference or, in this case, the arbor. Therefore large-arbor designs pick up more line with one revolution of the spool than does a spool with a traditional-sized arbor, thus allowing a faster retrieve than with a traditional reel.
The problem with some initial large-arbor designs was that only the size of the arbor increased - the overall circumference and width stayed the same. This seriously decreased the volume of the reel without adding to the speed of pickup.
Unfortunately, no universally accepted calculations exist for helping an angler determine exactly what lines and backing fit onto particular reels. Each manufacturer estimates line capacities differently, but most modern fly reels offer room for enough backing to do the job. And when in doubt, consider using gel-spun lines for backing, which can almost double the capacity of most reels.
One last spool feature that often is overlooked is the cranking diameter. The size of the arc created by turning the reel handle will determine whether you retrieve with your wrist or your arm. Anglers have their own comfortable handle diameter for efficient wrist retrieval. When the handle diameter exceeds this range, typically about 3.5 inches, the angler uses his arm to retrieve the line - a much slower and more tiring retrieve. Tests have shown that a fisherman can pick up line faster with a traditional-arbor reel using a wrist retrieve than with a large-arbor reel using an arm retrieve. To fix this, some manufacturers simply move the handle on larger reels closer to the center of the spool.
Opposite the spool on the reel sits the housing. This holds the axle around which the spool rotates, provides for the connection of the reel foot to the reel and helps guide the line in and out of the reel. Like spools, reel housings are either manufactured from solid stock materials like aluminum or assembled from various parts. With any assembled reel housing, the connections can potentially work themselves loose over time. Solid housings come in two styles - open and closed.
While there are exceptions, generally open designs allow anglers to palm the spool, while the closed designs do not. Most agree that closed designs afford more overall strength and better protection for the spool, but the closed-frame design demands an extremely refined manufacturing process because of the limited tolerances between the housing and the spool. More milling, deburring and polishing goes into a closed design to ensure a correct fit and to smooth surfaces that will come into contact with the line.
Other external components rarely given a second thought include the reel foot and the crank handle itself. The traditional reel foot places the reel directly under the reel seat and behind the casting hand, while one with a slight forward canter actually shifts the reel's center of gravity to directly below the hand. This small change makes the reel feel lighter than it actually is. Such a progressive foot (some manufacturers call this type of foot an arm) becomes particularly important on heavier reels. However, such a foot can lead to increased tangles when casting.
Most people view the crank handle as little more than a knob, but a poorly shaped handle can contribute to cramps when playing a fish. On antireverse or combination models, a poorly designed crank handle can even catch and foul the line during a cast or retrieve. Whether made from exotic woods, plastics or composites, the handle should be easy to grab and hold on to as well as remain comfortable during long fights. It should resist tangles, and on direct-drive reels should allow the fingers to slip free easily when a fish runs.