Nymph Leader
Start with 4 feet of .021, then add 1 foot of .015, then add 4 feet of .011 (0X), then add 6 to 8 inches of .007 (4X). If you want to add weight to the line to get the nymph down to the fish, place a weight between the 0X/4X junctions.
As to the two questions on your mind, what do I use and under what circumstances do I use it? Well, that depends on also two things. What are you fishing for and how clear is the water your fishing? Now, aren't you glad that you asked and even happier that I responded?
As a rule, the clearer the water, the longer the leader should be and the larger the fish, the larger the tippet should be on the end of your leader. Remember that your leader is what comes closest to the fish. Because of that, it is a critical factor in successful fishing, perhaps even more than the fly itself.
This is the most misunderstood part of the fly line to almost all anglers. Its' purpose is to reduce the visible connection between the fly and the fly line. Also, while we're repeating ourselves, this leader is about nine (9) feet in length but this length can vary depending on both the fish and the clarity of the water. The leader will transfer the strength of the cast smoothly towards the fly.
Don't let the numbering system fool you, because it is really backwards. Here is how it works. Since the size (diameter) of the small end is very important, (it must fit through the eye of the hook) a numbering system was devised to represent the diameter of the small end of the leader. In years past, most monofilament of the same diameter had pretty much the same breaking point (pound test). Anyway the size was more important.
Figuring no one wanted to learn the decimal system (.005) etc., they took the number eleven (11) and just arbitrarily started with that as the starting point and largest size. Eleventh thousandth equals 0X, ten = 1X, nine = 2X, eight = 3X, seven = 4X, six = 5X, five = 6X and four = 7X, the smallest size. Got all that? Sure you do. Well, the easiest way to remember is this, the bigger the number (7X), and the smaller the end of the leader is. IT'S BACKWARDS! BUT SO ARE THE FLIES, HOOKS, AND NOW, THE LEADERS.
At least they're consistent, somewhat; so deal with it and just shake your head, like the rest of us did but years ago. Oh, yes, now the tippets. They are just like the leaders. A 7X tippet will be the same diameter as the end of a 7X leader. That makes it easier to tie them together. Yup, you tie them together, at least a short section of tippet to the end of your leader. Why, you ask? Well, after several false casts, you discover little knots about a foot or so from your fly. These knots (wind knots) will create a very weak section in your leader that can break, causing you to loose fish and that's not a good thing and it's reason number one. Even as time goes by and you manage to cast better eliminating those wind knots, you'll be constantly cutting the tippet to put on that next killer pattern.
Each time you change the fly, you will loose about two (2) to three (3) inches of tippet material, so it is inevitable that you will have to replace the material lost to constant cutting, so there's the second and most common reason. These prepackaged leaders can cost about $2.00 to $3.00 a piece and constantly buying these required items, can get expensive. The tippet material comes in small spools, costing about $10.00 and each spool will have some 25 meters (decimal, sorry) or roughly 75 feet and that's a lot of small sections to tie on your leader (one tippet spool will be equivalent to nine (9) prepackaged leaders). The lesson here is obvious, save yourself some real money and tie on small sections of tippet material as needed.
The question of which leader size to use, can only be answered by personal preference; each angler must choose his or hers most effective length. There are certain guidelines that may be helpful in the leader length selection, listed below:
An often-asked question is, can you mix materials when building leaders? The only time that mixing nylon and fluorocarbon causes a problem is when the two sections are considerably different in diameter. Anglers have been connecting sections of nylon for years, without serious problems. Even with sections of like materials the problem arises only when the diameters of the two sections is great.
Remember that the need to connect different diameter section is the requirement that a leader has to have a stiff butt section connected to a limp tippet to which the fly is tied.
Arbors
The Arbor is the center area of the spool where the backing is tied onto and then wound around until the fly line is attached and that in turn is also wound around the arbor until all the line in safely stored onto the reel. The width of the arbor will determine its classification. The narrower arbor is called a standard arbor (SA), and the wider style is known as the Large Arbor (LA). Having said that, suffice it to say that the narrower arbor (SA) will hold less line and that line is stored in tighter coils on the spool. These characteristics create disadvantages when compared to the larger arbor (LA).
The larger the arbor the more efficient the reel is, because the actual fly line is further from the axis of rotation (center of the spool). The advantages are:
Larger Line Coils: This means less line memory.
Faster Retrieval Rate: The Fly Line occupies the Top % of the Spool.
Lower Running Speed: Less RPM on the fleeing felon.
Less Drag Force Increase: RPMs in relation to Resistance.