The Shimano GRX BL-RX810-L is a left-side hydraulic disc brake lever designed for drop-bar bikes, primarily gravel models. It’s a standalone lever (not a shifter/brake combo), so it’s used when building or upgrading a flat-mount hydraulic disc brake setup where only the lever is needed. This lever is compatible with Shimano GRX and compatible road/flat-mount hydraulic calipers, including BR-RX810. It uses Shimano mineral oil and is intended for use with drop bars that have a clamp diameter of 23.8–24.2 mm. It’s commonly paired with GRX RX810 or similar groupsets on 1×11 gravel and mixed-terrain builds. The lever features reach and free-stroke adjustment, a closed clamp design, and a textured anti-slip surface for better grip in wet or rough conditions. The aluminum lever body and composite housing keep weight reasonable while offering durability for mixed-terrain use.