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 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 motors (outside this tool's official fitment; the 1726.BL2 fits the Gen 2 lockring interface at 50 mm OD only)
• 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 (datasheet: D 50.8 mm, D1 46.4 mm, B 32 mm, B1 4.7 mm, SW 24 mm; weight 151 g)
• 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 Bosch Gen 2 chainring service, and the precision-machined fit at the lockring's 50 mm OD is what keeps the lockring's notches sharp across repeated service cycles.

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 →.

FAQ

Which Bosch motors does the 1726.BL2 fit? Bosch Gen 2 mid-drive motors: Active Line, Performance Line, and Performance Line CX from model year 2014 onwards, which mount the chainring with a 50 mm outer-diameter lockring. That is Unior's complete published fitment list for this tool.

Is the 1726.BL2 the same as the Bosch 0275009003 tool? Unior lists the 1726.BL2 as a replacement for the Bosch 0275009003 dealer-service tool. It engages the same Gen 2 chainring lockring and is CNC machined from premium flex plus carbon steel.

Can I torque the lockring with the 1726.BL2? Yes. The integrated 1/2 inch square drive accepts a torque wrench as well as ratchets and fixed handles, so you can install the lockring to the torque value Bosch publishes for Gen 2 motors. The tool weighs 151 g.

Does it fit Shimano STEPS, Fazua, or Bosch Gen 4 motors? No. Each e-bike system has its own lockring interface, and Bosch Gen 4 motors are outside this tool's published fitment. For Shimano STEPS, Unior makes the 1724.SSL; for the Fazua Ride 60, the 1724.FR60.