Fly fishing differs from other kinds of angling in that the weight of the line is cast rather than that of the lure. Fly rod lures have no appreciable heft. The line itself energizes the rod and then carries the fly to its destination.

Fly lines are bulkier and more apt to be alarming to the fish than those used for plug casting or spinning. Long monofilament leaders are used to disguise the fact that fly and line are connected.

A leader that collapses in a pile and leaves the fly floating near the line is not doing its job. Not only is the heavy line noticeable to fish but in case one is naive enough to take a fly, setting the hook would be extremely difficult.

Fly leaders are usually seven to nine feet long. The nine foot lengths are best for fishing small flies over wary fish and the shorter ones work well for bass and pan fish bugs.

In order to lie out properly, leaders are usually tapered from a relatively large diameter butt to a slender point or "tippet" that allows the fly to swim or drift naturally.

Tapered leaders, of course, can be purchased. They are usually knotless and available in various tippet sizes. Berkley has good ones at reasonable prices.

You can, however, easily make your own, tailored to your personal fishing requirements. Here are a few simple guidelines and the reasons for them.

First of all in leaders more than five feet long, the less flexible butt section should make up roughly two-thirds of the whole. Pound test is of no consequence here. What is important is stiffness.

The leader should be an extension of the fly line. In order to unroll with and lie out like part of the line, the two must flex at the same rate.

In other words there must be no "hinge" where the two join. A leader stiffer than the line will cause the line to alight with its end turned back. If too limp, the leader and fly folds back.

To check for comparative flexibility, grasp the line about ten inches from the leader connection and grip the leader about the same distance from the line. Now bring your hands together slightly and make an upright semi-circle of line and leader. The bow thus formed should be continuous and sag-free.

As a general rule monofilament somewhere between .015" and .020" diameter will make satisfactory leader butts for most fly lines. Last summer I picked up a spool of Sunset spinning line. It is stiff enough to work well with my 4 and 5 level and 6 and 7 weight-forward lines. The 460 yard spool should make a lot of leaders.

Different brands do vary in flexibility. Probably the best idea is to fasten a piece to the line and try it as described above. The smallest diameter that will turn over and lie out well is the most desirable.

A line to leader connection that hinges will also keep leader and fly from unrolling properly when cast. I personally prefer a nail knot here. Epoxy splices or using epoxy to lock the knot will usually result in a stiff enough joint so that the line cracks just back of the connection thereby making a hinge.

I like to coat leader to line knots with Goodyear Pliobond. It stays flexible. The tippet must be limp so diameter here of course is important. Pound test, except possibly for fishing contest requirements isn't. Fly size, not fish size, determines tippet diameter. Too large will make a fly swim or float like it is attached to a stick. Too fine will tangle or half-hitch around the fly when cast.

The "X" rating of leaders is confusing. It refers to diameter, not strength. It is a carry over from the days of silk worm gut when material was sized by drawing through holes in a steel plate.

The holes had sharp edges that shaved the gut and were graduated in thousandths of an inch. They started at OX, which is 0.011. The X designated which hole was used for final sizing.

Specifying diameters in thousandths is gradually replacing the old X system and most tippet material spools are labeled with both.

Experience will show what sizes work best for your fishing. Be sure to buy material made expressly for tippets. You will be reasonably certain of obtaining limp material with maximum knot strength.

Just for starters, 4X or 0.007 is probably the most poplar diameter. It works well with most size 12 or 14 flies although a bushy wind-resistant twelve might require an 0.008 (3X) leader. Size 16 and 18 work with .006 tippets. More delicate flies require still finer diameters.

Traditionally, tapered leaders are made by tying sections together with blood knots. They do not hold well when monofilament diameters vary over .002 of an inch so with these knots it's necessary to use several sections.

Factory made knotless leaders have followed the same long taper design for no good reason.

Of late, however, the trend has been towards surgeon's knots. They are easy to tie, less bulky and hold vastly different diameter monofilament without slipping.

Here's a simple recipe for a nine foot leader that will lay out as straight and gently as any you have ever used.

Butt: 6 feet of .018" monofilament, step down section: 1 foot of 0.011"(OX), tippet: 2 feet of 0.007" (4X), using two surgeons knots.

Tied with blood knots, the step down from butt to tippet alone would require several sections.

Other lengths will use the same proportions. For windy fishing, shorten the tippet. Nothing says the tippet diameter is written in stone either. Go smaller or larger to accommodate fly size.

All this applies to floating lines. Leaders for sinking lines are even simpler. All you need for them are three feet or so of tippet material. Long leaders let the fly ride way above the line. Fish aren't as wary of sunken lines.

Carry a piece of inner tube rubber in your vest or tackle box and some monofilament in two or three sizes. It's a simple thing to change tippets and pulling the leader through a fold of rubber will take out kinks and spirals.