Bosch Gen 2 Lockring Tool

Bosch's eBike Systems mid-drive motors; Active Line, Performance Line, and Performance Line CX from model year 2014 onwards; mount their chainring on the motor spindle via a proprietary lockring with a 50 mm outer diameter. A standard cassette lockring or BB socket won't engage; the Bosch Gen 2 lockring is a specific engagement pattern that Bosch's own dealer-service tool (0275009003) was designed to service. The 1726.BL2 is the shop-bench replacement for that tool.

CNC-machined from premium flex plus carbon steel, the 1726.BL2 fits the Bosch Gen 2 lockring's 50 mm OD without rocking play. An integrated 1/2" drive at the head accepts a torque wrench for the install-spec torque Bosch publishes, plus the standard ratchets and fixed handles a shop bench uses for general turning.

Why a Bosch-specific tool exists

Bosch's chainring-mounting design on Gen 2 motors uses a lockring rather than a chainring-bolt assembly, because the motor's spindle has to support both the chainring and the pedal drive load through a single threaded interface. The lockring's outer engagement is sized to a specific notch profile Bosch chose for the dealer tool; aftermarket cassette lockring tools don't fit it. A workshop that services Bosch-equipped e-bikes; the largest installed base on US IBD-channel e-MTBs; needs a tool sized to this specific lockring.

Compatibility

• Bosch Active Line motors (2014+)
• Bosch Performance Line motors (2014+)
• Bosch Performance Line CX motors (2014+)
• Bosch Gen 2 chainring lockrings at 50 mm OD
• Replacement for Bosch dealer-service tool 0275009003
• Not for Bosch Gen 4 motor-mount bolts (those use Torx Plus T40, which needs a dedicated Torx Plus driver rather than a standard Torx tip; the recess geometry is flatter)
• Not for Shimano STEPS, Fazua, Yamaha, Brose, or Bafang motors (each has its own lockring tool)

Specs

• Material: premium flex plus carbon steel, CNC-machined
• Drive: 1/2" square drive (use with a torque wrench, ratchet, or fixed handle)
• Lockring fit: Bosch Gen 2 chainring lockring, 50 mm OD
• Includes: the tool itself

Built in Zreče

Unior has been forging hand tools in Zreče since 1919, and sponsors professional road and mountain-bike race teams. The 1726.BL2 is the workshop tool for the largest single segment of the US e-bike market; Bosch-equipped builds on the IBD channel; and the precision-machined fit at 50 mm OD is what keeps the lockring's notches sharp across multiple service cycles, which on an e-bike workshop with regular Bosch service is a service-life concern the original dealer tool wasn't sized for.

Pro tip from our mechanics

The Bosch chainring lockring sometimes seizes after long service intervals, especially on e-bikes ridden through winter conditions. Before applying loosening torque, clean the lockring's outer notches with a soft brush and apply a small amount of penetrating lubricant at the lockring-to-spindle interface from behind the chainring. Let it work for several minutes. The lockring backs off cleanly with the lubricant in place; without it, the notches can round under the breakaway torque a seized lockring needs.

For what changes about service intervals, torque values, and procedures on e-bike drivetrains: Servicing an e-bike: what's different from an analog bike →.