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 is the official technical partner of multiple World Tour and downhill 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 →.