A: You need a special leader for permit because you hold the fly line at the ready-to-cast position, and a crab fly is tough to throw with little line out of the rod tip. I suggest building an entire leader from the same manufacturer's material - most often high-quality monofilament. To make a leader between 10 and 11 feet long, the butt section should be 50-pound test that is heavy yet limp and measures half the total length of the leader. You want the leader to unroll just like the fly line, and a stiff butt section does not turn over easily. Next use 40-, 30- and 25-pound test in decreasing lengths and then add a tippet of 20- or 16-pound test. Never make the tippet longer than 18 inches or you may get wind knots in it.