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Ernie Ball 7-String Slinky Cobalt Custom (.009–.062): the Schecter KM-7 / Hauch lighter-top 7-string

Reviewed by the Change Your Strings editorial team ·

The .009–.062 Cobalt 7-string is a non-stock custom gauge: a .009 plain top for shred-friendly bending paired with a .062 low string for Drop G# rhythm definition. Schecter ships this exact set factory-strung on the KM-7 MKIII Keith Merrow signature; Wes Hauch builds his 7-string Cobalts to the same recipe. Cobalt voicing through passive pickups (Fishman Fluence, EMG, Bare Knuckle): tighter low-string definition, brighter upper-mid push that helps the picking hand articulate fast lines without losing rhythm-side weight.

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Anatomy

Tone

Voicing through a passive 7-string pickup

Why the asymmetric gauge

The .009-.062 7-string Cobalt is a deliberate asymmetric choice. A balanced gauge (e.g., the stock 2730 .010-.062) gives you firm rhythm and firm leads. A light-balanced gauge (.009-.054 or .010-.056, like the 2729) gives shred-friendly leads but loses low-string definition for heavy rhythm. The .009-.062 splits the difference: shred-friendly on top, rhythm-firm on bottom.

This works because:

  • The high strings are the lead voice. Light top = effortless fast picking, wide bends, expressive vibrato. Same logic that made .009 popular for 6-string shred since the 1980s.
  • The low strings are the rhythm voice. Heavy bottom = pitch-stable Drop A / Drop G# under high gain, no flap on palm-muted chug.
  • Modern 7-string compositional architecture often separates the two. Solo prog-metal players write rhythm passages and lead passages on the same instrument; the asymmetric gauge serves both.

Who plays this set

Keith Merrow is the documented anchor. His Schecter KM-7 MKIII Artist signature ships factory-strung with this exact .009-.062 Cobalt configuration; Schecter and Sweetwater product documentation both call out the gauge. Merrow's solo catalog (instrumental prog-metal, fast melodic phrasing, Drop A and Drop G# rhythm) is exactly the use case the asymmetric gauge was tuned for.

Wes Hauch (Alluvial, ex-The Faceless, Thy Art Is Murder) runs the same .009-.062 Cobalt recipe per Equipboard and Wired Guitarist gear coverage. Hauch quote on Cobalts: "best strings ever." His material spans technical death metal and djent on 6-, 7-, and 8-string; on 7-string, the .009-.062 is his go-to.

Both pros independently arrived at the same asymmetric configuration, which is part of what validates it as a thoughtful gauge choice rather than a one-off.

Best for

  • Solo instrumental prog-metal on 7-string. Lead-fluid playing with Drop A / Drop G# rhythm passages.
  • Schecter KM-7 MKIII players. This is the factory-strung set; replacement keeps the guitar feel consistent.
  • Players who want Steve Vai-style 6-string light-top feel translated to 7-string.
  • Drop A or Drop G# tunings primarily. The .062 is calibrated for those specifically.

Worst for

  • B standard 7-string unless you specifically want a noticeably-loose top. The .009 plain in B standard sits at very light tension; many players find it too soft for chord-style playing.
  • Beginners. The asymmetric gauge is a deliberate optimization for advanced players who know which strings they're emphasizing in their playing.
  • Quad-tracked rhythm-heavy production work. A balanced .010-.062 (SKU 2730) is the cleaner choice for rhythm-only contexts.

Install and break-in

The .009 plain top requires a properly cut nut slot, most production 7-strings cut their nut for .010 or .011 plain on top. The KM-7 MKIII is cut for .009 from the factory. On other 7-strings, the .009 may sit slightly low in the slot and rattle; a luthier can ream the slot to spec.

Break-in: 30–45 minutes. The .009 plain settles fastest of any string in the set.

Verdict

The .009-.062 Cobalt 7-string is a deliberate, niche, and correct gauge for a specific kind of 7-string player: the solo or duo instrumental prog-metal player who writes lead-heavy melodic material against Drop A or Drop G# rhythm passages. Keith Merrow and Wes Hauch independently chose the same recipe; Schecter ships it factory-strung on the KM-7 MKIII because the gauge fits the artist's playing.

If your music sits in this lane, build the set (buy a 2730 plus a .009 single, or order custom through Ernie Ball, or pick up a KM-7 MKIII new). If your playing is rhythm-heavy or your tuning is B standard, the stock 2730 or 2729 is the right answer.

Affiliate link not applicable for this gauge. The .009–.062 7-string Cobalt is not a retail Ernie Ball SKU. Consumer purchase paths: Schecter KM-7 MKIII Artist (factory-strung); Ernie Ball custom string program; or assemble from a 2730 set plus a .009 single pack. ProductCard suppressed accordingly.

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