Ernie Ball Hybrid Slinky Cobalt Bass (.045–.105) review: Rex Brown's Pantera low end

Ernie Ball's Hybrid Slinky Cobalt Bass takes the familiar Hybrid Slinky bass gauge, .045 to .105, and winds it in a cobalt alloy instead of nickel-plated steel. Ernie Ball's own description of the Cobalt line calls it engineered "to maximize output and clarity," built to give bassists "an extended dynamic range, incredible harmonic response, increased low end, and crisp, clear highs." The company's claim: cobalt creates a stronger magnetic relationship with pickups than any other alloy it has shipped.

It's also a documented touring-pro gauge, not just marketing copy. Premier Guitar's 2024 Rig Rundown on Pantera found this exact set on bassist Rex Brown's signature Gibson Thunderbird: "This one (and other 4-strings) ride with Ernie Ball 2733 Hybrid Slinky Cobalt Electric Bass strings," in the outlet's own words.

Hybrid Slinky sits in the middle of Ernie Ball's broader 4-string nickel Slinky bass family, which runs Extra Slinky (.040–.095), Hyper Slinky (.040–.100), Super Slinky (.045–.100), Hybrid Slinky (.045–.105), Regular Slinky (.050–.105), Power Slinky (.055–.110), and Beefy Slinky (.065–.130). Cobalt takes that same Hybrid gauge and changes only the wrap-wire alloy, not the tension profile, so anyone already comfortable on nickel Hybrid Slinky Bass drops straight into this set with no setup surprises.

For the fully measured Cobalt vs nickel breakdown (output dB, brightness curve, longevity, bend feel), see Cobalt vs nickel Slinky: the voicing difference, measured. That comparison is built on Ernie Ball's guitar Cobalt line: the wrap-wire alloy and Ernie Ball's marketing claims carry over to bass, but CYS hasn't independently measured bass-specific numbers.

Ernie Ball ships more than one Cobalt bass gauge. This set is the Hybrid Slinky, the lighter-top option:

• Lighter top, same low string: Hybrid Slinky Cobalt Bass (this set), .045–.065–.085–.105.
• Heavier top, same low string: Regular Slinky Cobalt Bass (SKU 2732), .050–.070–.085–.105. Same A and E strings, heavier D and G.
• 5-string: Ernie Ball 5-String Regular Slinky Cobalt Bass (.045–.130, MPN P02736), the gauge Premier Guitar cites for Rex Brown's 5-string Spector: "the 5-string Spector takes Ernie Ball 5-String Slinky Cobalt Bass Strings (.45–.130)." Not simply this 4-string set plus a low B; the middle strings step down slightly to balance the added B.

Full picture of how the Cobalt name works across Ernie Ball's whole catalog: Cobalt Slinky gauges explained.

Pantera bassist Rex Brown strings his signature Gibson Thunderbird, built around a mahogany body, mahogany set neck, rosewood fretboard, and Gibson's Rexbucker Thunderbird humbuckers, with this exact set. Premier Guitar's Chris Kies wrote it directly in the outlet's 2024 Rig Rundown: "This one (and other 4-strings) ride with Ernie Ball 2733 Hybrid Slinky Cobalt Electric Bass strings." Brown's full gear breakdown, strings through pedalboard, is on his CYS bassist profile.

Brown's other main bass, a 2023 Spector NS-5, runs a different gauge instead: Ernie Ball 5-String Regular Slinky Cobalt Bass, .045 to .130. Same Cobalt technology, a purpose-built 5-string spread for the extra low B, not just this 4-string gauge with a string added.

For the full documented roster of Ernie Ball Cobalt users, guitar and bass, see Who plays Cobalt Slinky strings: the documented pro users.

• Standard-tuned rock and metal bass that wants Cobalt's output and low-end bump without stepping up a full gauge size. Pantera's Rex Brown is the clearest documented example, running this exact set live on his signature Thunderbird.
• Passive-pickup basses. The magnetic-response claim behind Cobalt's voicing shift matters most on a passive pickup; an active preamp already adds its own gain and EQ, so some of the Cobalt bump gets masked by the preamp's own coloring.
• Players who want an easier top string than Regular Slinky Cobalt Bass. The .045 G string is 10 percent thinner than Regular's .050, a real difference for fast fingerstyle runs and light-touch tapping.

• Players chasing maximum string life. Cobalt is uncoated, same wear curve as any uncoated roundwound; Ernie Ball's own longevity line is Paradigm (Everlast nano-treatment), not Cobalt.
• Heavy drop-tuned bass. The .105 low string is a standard-tuning gauge. A 5-string Cobalt set, or a heavier 4-string like Power Slinky, handles Drop D and below with more authority.
• Anyone who wants the cheapest bass string on the shelf. Cobalt costs more per set than Ernie Ball's standard nickel Slinky bass line at the same gauge.

Because the A and E strings match Regular Slinky Cobalt Bass exactly, a bass already set up for .050–.105 needs only a light nut-slot check on the G and D strings when switching to this .045 top. Break-in runs about the same as any fresh roundwound, 15 to 20 minutes of playing before the top end settles. Stretch each string, pull up gently a few times, retune, repeat, before a gig or session.

Hybrid Slinky Cobalt Bass is Ernie Ball's lighter-top answer inside its Cobalt bass line: the same .105 low string and cobalt-alloy output bump as Regular Slinky Cobalt Bass, with an easier .045 G string on top. It's a real touring gauge, not just a catalog filler. Rex Brown runs it on the signature Thunderbird he plays across Pantera's reunion shows.

If you're coming from a standard nickel bass set and want more output and low-end presence without changing gauge, this is a straightforward upgrade. If you're chasing the lowest price per set instead, the nickel Regular Slinky Bass costs less for a comparable standard-tuning gauge.

Ernie Ball

Hybrid Slinky Cobalt Bass (.045–.105)

.045 – .105

Price tier: $$

Why this one: Rex Brown's documented Pantera gauge: cobalt-alloy output and low-end bump on a standard .045 to .105 4-string bass set.

E Standard (4-string)Eb Standard (4-string)Metal

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