Micro leaders for euro nymphing: what they are, in millimetres

A micro leader is a euro nymphing leader whose long butt section is much thinner than usual, 0.20 to about 0.25 mm (5 to 8 lb) instead of 0.43 mm (20 lb). It weighs less in the air between the rod tip and the water, so it sags less and pulls the fly less. In return it is harder to cast, poor with dry flies and, by some accounts, worse in wind. Leaders for euro nymphing are one of the things I teach in competition training, and this article gives the numbers behind the choice.

The method below is the published craft, with the sources named. What I add, from more than ten years of competitive fly fishing, is the angle most pages skip: how long a leader may be, and what it has to be attached to.

What “micro” means: no fixed definition, three thicknesses

There is no agreed line where a leader becomes “micro”. Each writer and each shop draws it in a different place:

• Troutbitten names three steps: Standard at 20 lb (0.43 mm), Thin at 10 lb (0.30 mm) and Micro-Thin at 5 lb (0.20 mm) (Swentosky, 2021).
• George Daniel’s ultra-thin rig is a 6 lb butt (Daniel, 2023).
• AvidMax’s micro-thin starts at 8 lb (Beaulieu, 2020).
• Fly Fish Food sells a “Micro Thin” of straight 6 lb mono (Fly Fish Food leaders).
• Tactical Fly Fisher’s three leaders are 20, 15 and 12 lb, named Thin, Thinner and Thinnest (Tactical Fly Fisher leaders).

So one shop’s “thinnest” is thicker than another’s “thin”. Ask for the diameter in millimetres, not the name. For Maxima Chameleon, the butt material most of these formulas use, 20 lb is 0.43 mm, 10 lb is 0.30 mm and 5 lb is 0.20 mm; 6 and 8 lb sit between 0.20 and 0.30 mm (diameters as Troutbitten gives them, converted from inches).

Diameters for 6 and 8 lb are approximate; read the spool.

Sag: why thinner drifts better

Between the rod tip and the water the leader hangs in a curve under its own weight. That curve pulls the flies towards you and off their line. It is drag, as much as a fly line on the water is drag. It is worst just after the cast, when the fly is furthest away, and when you reach across current seams (Swentosky, 2021).

A lighter leader hangs less. That is the whole argument for a micro leader, and it is a good one: less sag, longer drifts with light flies, a straighter line from rod tip to fly, and better feel of the bed and of some takes (Swentosky, 2021). George Daniel adds that an ultra-thin rig gets deeper with less weight and makes a take easier to tell from the bottom (Daniel, 2023). On big rivers it lets you reach further seams (Beaulieu, 2020).

What the leader weighs: 0.55 g against 0.20 g

Troutbitten put the leaders on a scale. With 14 ft (4.3 m) of leader outside the rod tip and 4 ft (1.2 m) of 5X tippet, the standard leader weighs about 0.55 g, the thin one 0.42 g and the micro-thin 0.20 g. At 24 ft (7.3 m) outside the tip, the standard weighs almost three times the micro-thin (Swentosky, 2021).

Now set that beside a fly. A 3.0 mm tungsten bead weighs about 0.2 g (see how heavy should a euro nymph be). At distance, a standard leader outweighs a light fly two or three times over. The leader, not the fly, decides where the fly goes. A micro leader puts the fly back in charge.

Published formulas side by side

These are the recipes as the authors published them, in their units and converted. I built the table from the sources named; none of these is my own leader.

Two things stand out. Three of the five are long, about 10 to 12 m, and replace the fly line altogether; Fly Fish Food’s is 4.3 m. And on these rigs the sighter is no thicker than the butt: 3X is 0.20 mm, the same as the 5 lb butt, and Daniel’s 3X or 4X sighter is thinner than his 6 lb butt.

What you give up

Casting

A thin leader has almost no mass of its own, so the weight of the fly makes the cast. Tuck casts and curve casts are hard. Accuracy holds only in a narrow arc. The lightest flies often need a water haul, loading the rod against the surface, to go anywhere (Swentosky, 2021). George Daniel compares it to spin casting (Daniel, 2023). The butt has to be about 10 to 12 lb before a mono leader casts like a fly line at all (Swentosky, 2019).

Wind

Sources disagree. AvidMax says a thinner leader gives the wind less to push (Beaulieu, 2020). A reader there, and Tactical Fly Fisher’s own leader notes, say thin leaders are harder to control in wind. Both can be true at once: less surface for the wind to catch, but less mass to drive the cast through it.

Dry flies and dry-dropper

George Daniel says an ultra-thin rig cannot cast dry flies or wind-resistant indicators (Daniel, 2023). Swentosky lists dry-dropper among the things the standard leader does and the thin ones do not (Swentosky, 2021). Devin Olsen is shown fishing a dry-dropper on a micro leader in a Fulling Mill film (by the film’s description; MidCurrent, 2024). The fair statement is that it is possible in skilled hands and is not what the leader is for.

Handling and wear

Thin, slick mono is hard to hold in the line hand, worse with cold fingers, and it slips through an open-frame reel, so a full-cage reel is advised; the rig suits 2 and 3 weight rods (Daniel, 2023). Readers of Troutbitten report a shorter life, with the butt needing straightening after a few trips, and worry about breakage with big fish; those are readers’ comments, not the author’s (Troutbitten podcast, 2023).

Tippet match

A 4 to 6 lb butt is a poor match for heavy tippet. George Daniel goes up to a 15 lb butt with 3X when a big river asks for it (Daniel, 2023). The butt, the sighter and the tippet have to make sense as a chain.

The rod and the reel

A 2 or 3 weight euro rod, and a reel whose frame does not let thin mono slip between the spool and the cage (Daniel, 2023). If you do not own that, a euro nymph kit can be rented by anglers fishing with me, and modern competition rods and reels at an additional charge: see gear rental.

Micro leaders under competition rules

This is where the US articles stop and a competition angler has to start. Under the FIPS-Mouche rules, 2025 edition:

• the leader, tippet included, may be at most twice the length of the rod, except in lake and dry-fly sectors (article 28.1): 6.1 m (20 ft) on a 10 ft rod, 6.7 m (22 ft) on an 11 ft rod;
• it must be attached to a fly line at least 0.55 mm thick and 22 m long (articles 27.1 and 27.2);
• knots in the leader must be at least 30 cm apart (article 28.2);
• nothing that floats or sinks may be added to the leader (article 28.3).

So a competition micro leader is a short, thin leader on a thin fly line, not 26 ft of mono to the backing. Tactical Fly Fisher sells its leaders at 25 ft (7.6 m) and tells competitors to cut them to length (Tactical Fly Fisher leaders). Swentosky’s account is that the tackle trade answered the length rule with thin competition fly lines, and that some anglers went to micro-thin leaders to cut sag further (Swentosky, 2020). Those are competition rules, binding only in competition. The whole rule set, article by article, is in FIPS-Mouche rules explained.

When to fish one, and when not

Swentosky’s own answer is that there is no hierarchy: a 5 lb rig is not better than a 20 lb rig, skill with either matters more, and he reaches for thin leaders with light flies, under about 0.30 g, at roughly 6 to 11 m (20 to 35 ft) (Swentosky, 2021). George Daniel calls thin mono deadly for euro nymphing within its limits (Daniel, 2023). Put side by side, the sources say:

• Micro leader: light flies under about 0.30 g, at roughly 6 to 11 m, nymphs only (Swentosky, 2021; Daniel, 2023).
• Standard leader: heavier flies, dry-dropper, tuck casts, and changing method without changing the leader (Swentosky, 2021).

For European grayling in particular, none of the sources found for this article treats micro leaders on their own. The nearest is Dave Southall’s grayling set-up: a 0.55 mm micro nymph line, a 7 ft (2.1 m) tapered leader, a 15 in (38 cm) sighter and 0.13 mm tippet (Sunray). That is a short leader on a thin line, close to the competition shape, for fish that sit close in clear, shallow water. How the fish take is in grayling vs trout: lies and takes.

Leaders in competition training

Training covers what you want to work on, and the leaders for euro nymphing and for dry flies are on the list. Practice sessions are fished against the clock, as in a competition. The rivers I guide are grayling rivers; the Ćehotina is, in my words, a wild euro-nymphing river, and the Lim is the one I name first for a first day. River by river, the nymph is in euro nymphing in Montenegro.

The other numbers of the rig are in leader, sighter and tippet length and one nymph or two. For the country as a whole, start with fly fishing in Montenegro: the complete guide.

Questions

What is a micro leader?

A euro nymphing leader with a very thin butt, roughly 5 to 8 lb mono (about 0.20 to 0.25 mm), in place of the usual 15 to 20 lb (Swentosky, 2021; Daniel, 2023; Beaulieu, 2020).

Why does a thin leader drift better?

It weighs less in the air, so it sags less between rod tip and water and pulls the fly less (Swentosky, 2021).

Is a micro leader harder to cast?

Yes. The leader has almost no mass, so the fly’s weight has to make the cast; tuck and curve casts are hard (Swentosky, 2021; Daniel, 2023).

What rod and reel suit a micro leader?

A 2 or 3 weight euro rod, with a full-cage reel so the mono cannot slip behind the spool (Daniel, 2023).

Is a micro leader allowed in competition?

Yes, if the whole leader is no longer than twice the rod and sits on a fly line at least 0.55 mm thick (FIPS-Mouche rules, 2025 edition, articles 27.1 and 28.1).

Can I fish a dry-dropper on a micro leader?

Skilled anglers do, but the leader is not built for it; the standard leader is the one Swentosky lists for dry-dropper, and Tactical Fly Fisher says its thinnest leader casts one less easily (Swentosky, 2021; Tactical Fly Fisher leaders).

The numbers tell you what a thin leader does. Which one to tie on for the river, the wind and the fly in front of you is learned on the water, and I teach it in competition training or on a guided day. Tell me your dates and what you want to work on. Request your dates.