Ernie Ball Super Slinky Cobalt (.009–.042) review: the light-gauge Cobalt set

Reviewed by the Change Your Strings editorial team · 2026-07-16

Ernie Ball Super Slinky Cobalt (2723) is the .009–.042 light-gauge set in the Cobalt line. Cobalt-iron wrap on a tin-plated steel hex core gives passive pickups roughly 2–3 dB more output and a tighter upper midrange than nickel Super Slinky at the same gauge. Steve Vai is the documented anchor user. Pick it for shred-lead E standard, vibrato-heavy rock, and any context where you want the lightest practical Cobalt for fast picking and wide bending.

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Anatomy

SKU: Ernie Ball 2723
MPN: P02723
Gauge: .009 – .042 (Super Slinky)
Gauge set: .009, .011, .016, .024, .032, .042
Core wire: Tin-plated hex steel
Wrap wire: Cobalt-iron alloy
Plain strings: Tin-plated hex-core steel (.009, .011, .016 plain)
Coating: None, uncoated
Winding: Standard roundwound
Intended scale: 25.5" (Ibanez JEM, Strat) primary; 24.75" Gibson works for slacker feel
Intended tunings: E standard, Eb standard (with looser feel)
Total tension (25.5", E standard): ~85 lbs
Total tension (25.5", Eb standard): ~76 lbs (looser, floppier under hard picking)
Launched: January 2012 (Cobalt line debut)
Package: Single pack and 3-pack

Tone

Voicing through a passive pickup

Output: 2–3 dB louder than nickel Super Slinky. Most pronounced when running into a clean amp; less audible into a saturated high-gain rig.
Top end: More present 2–4 kHz region. Lead notes have more bite without the EQ tweaks players sometimes apply to nickel .009 sets to make them cut.
Low end: Tighter pick attack on the wound strings. The .032 and .042 don't bloom under fast palm-muted runs.
Bend feel: .009 plain on top is the most bendable standard 6-string gauge. Cobalt wrap doesn't change bend feel; the voicing change happens through the amp, not in the hand.

Where this set sits in the Cobalt range

Super Slinky Cobalt is the lightest standard 6-string Cobalt:

E / Eb standard, lead-heavy or beginner-friendly: This set, Super Slinky Cobalt (.009–.042).
E standard, the in-between gauge: Primo Slinky Cobalt (.0095–.044), a half-gauge step for players who never settled on .009 or .010.
E / Eb standard, balanced: Regular Slinky Cobalt (.010–.046).
Eb standard / Drop D: Power Slinky Cobalt (.011–.048).
Light top, heavy bottom: Hybrid Slinky Cobalt (.009–.046) or Skinny Top Heavy Bottom Cobalt (.010–.052).
Drop C# / Drop C: Beefy Slinky Cobalt (.011–.054).

Picking guide: Cobalt Slinky gauges explained.

Who plays this set

Steve Vai is the documented anchor user of this gauge. Shortly after Ernie Ball launched the Cobalt line in January 2012, Vai talked about the new Cobalt Super Slinky on the record: "They move more with my emotional input." His primary instrument is the Ibanez JEM (25.5-inch scale, Evolution pickups). He plays E standard for most material; in his own words he's "usually a 9-42 guy," stepping up to .010s only for specific songs tuned down a whole step, like "John the Revelator" and "Gravity Storm." The 9-42 gauge itself has stayed consistent across Vai's on-record Ernie Ball interviews over the years; the specific wire line he name-checks has varied (Cobalt at the 2012 launch, Paradigm in a more recent Ernie Ball podcast appearance).

Other documented light-gauge Cobalt users span the broader 6-string Cobalt roster, see Cobalt pro roster.

Best for

E standard lead-heavy playing. Shred, modern instrumental, fusion lead lines.
Eb standard with looser feel. Vai-style vibrato, multi-step bends, behind-the-nut moves.
Beginners on a 25.5-inch scale guitar. Lightest practical gauge for early bending without buzzing.
Picking-precision drills. The cobalt wrap's upper-mid push reveals attack inconsistencies, useful for practice.

Worst for

Drop tunings of any kind. The .042 low string flaps in Drop D and below.
Heavy palm-muted rhythm work. .032 and .042 don't have the mass to hold attack against quad-tracked production.
Acoustic-style hybrid picking with thumbpick. Light wound strings get pulled out of intonation by aggressive thumbpick attack.
Players who break .009s frequently. Step to .010s for durability; same Cobalt voicing in Regular Slinky Cobalt.

Install and break-in

Going from .010s to .009s drops total tension by roughly 6–8 pounds. The neck will pull back slightly with less string pull, which usually wants a quarter-turn truss-rod tighten to compensate. Nut slots accept .009s without filing if they were cut for .010s; intonation should be reset.

Break-in: 20–30 minutes of playing before the bright initial top end settles. Stretch each string before that.

Verdict

Super Slinky Cobalt is the lightest practical Cobalt set in the Ernie Ball catalog. If you play E standard or Eb standard, lean lead-heavy, want a shred-friendly bend feel, and want the cobalt voicing's extra output and upper-mid bite through a passive-pickup rig, this is the set. It's the gauge Steve Vai has cited in Ernie Ball's own artist coverage for years, including at the Cobalt line's 2012 launch.

Pick this over nickel Super Slinky if you A/B them and hear the cobalt push as something useful for your tone. If you're not sure, demo nickel and Cobalt back-to-back and pick by ear; both work.

Ernie Ball

Super Slinky Cobalt (.009–.042)

.009 – .042

Price tier: $

Why this one: The light-top Cobalt for E standard: .009 plain strings for fast bends and shred articulation, plus the Cobalt output bump.

E StandardEb StandardRock

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**Voicing comparison:**Cobalt vs nickel Slinky: the voicing difference, measured **Cobalt range gauge guide:**Cobalt Slinky gauges explained **All 5 Ernie Ball wire lines:**Slinky vs RPS vs M-Steel vs Paradigm vs Cobalt **Cobalt line roster:**Who plays Cobalt Slinky strings **Artist rig:**Steve Vai's Cobalt rig, sourced

Frequently asked questions

Are Super Slinky Cobalts good for beginners?

Yes. .009 plain top is the lightest standard 6-string electric gauge most beginners can play comfortably without buzzing out. The cobalt wrap makes the wound strings a touch louder than nickel through the same amp, which can help a beginner hear pick-attack mistakes and self-correct. The downside is .009s break easier than .010s under heavy picking.

Why does Steve Vai play .009s instead of .010s?

Vai's lead vocabulary depends on extreme vibrato, multi-step bends, and behind-the-nut bends. The lighter .009 plain top makes those moves possible at the speed and intensity he plays them. He has discussed the choice on the record about Cobalts: 'they move more with my emotional input.' At his playing intensity, .010s would fight back.

Will .009s flap in Eb standard?

Slightly. Eb-tuned .009s sit at about 89% the tension of E-tuned .009s, noticeably floppier on hard rhythm picking. For Eb standard, most players step up to .010s (Regular Slinky Cobalt) or stay on .009s and accept the looser feel for the bending advantage.

How do Cobalts compare to nickel Super Slinky?

Same gauges, different wrap voicing. Cobalts: ~2–3 dB louder through passive pickups, more present 2–4 kHz region, slightly tighter low-end response. Nickel Super Slinky: smoother top end, slightly warmer overall. Both are uncoated and last about the same (1–3 weeks of daily play before brightness drops). Cobalt is a voicing decision, not a longevity upgrade.

Will .009s work in Drop D?

The .042 low string in Drop D sits at about 11 pounds tension, soft and flabby for hard rhythm work. Use Skinny Top Heavy Bottom Cobalt (.010–.052) or Power Slinky Cobalt (.011–.048) for Drop D. Super Slinky is for E standard and Eb standard primary play.

Are Cobalts better for shred than nickel?

Better isn't the right word, voicing different. The cobalt wrap's harder upper-mid push helps fast-picking patterns sit forward in a band mix. Nickel's smoother top can feel more vintage-Strat-like under fast picking. Pick by ear, not by spec sheet. Vai's Cobalt Super Slinky runs .009s; Yngwie Malmsteen's Fender signature nickel set is a shade lighter at .008s. Both shred fine at their own gauge.