7x8mm Open End Combination Wrench

Pull a Shimano caliper off a hydraulic disc-brake bike for a bleed and you'll meet either a 7 mm bleed screw or an 8 mm one, depending on which model is bolted to the frame. The dust cover hides the size until you've already committed to the job. The 7x8mm Open End Combination Wrench keeps that detail from costing you a trip back to the bench: both sizes live on one tool, and the wrench in your hand fits the screw on the caliper either way.

The two open-end heads are sized to seat fully on the bleed screw's flats before you apply torque. Bleed screws are soft metal and they round when a wrench corners against them at a sloppy angle, which is the slow way to learn that a hydraulic brake bleed has just become a $40 caliper replacement. A wrench that matches the flat-to-flat dimension snugly is the first guard against that outcome. The forged steel body holds its tolerance even after the wrench has lived in a working drawer for a few seasons.

Open-end geometry is the right call for a bleed screw because there's no hydraulic line running through the fitting; you can slide the wrench on and off without weaving it around anything. That's not the case at the compression nut, where the line passes through the wrench and a slotted flare-nut design is what you want. The 7x8 is the bleed-screw wrench in the Unior hydraulic-brake kit; the flare-nut wrenches are the line-side tools, and the three together cover the whole service.

Specs

• Function: open-end combination wrench for hydraulic disc-brake bleed screws
• Sizes: 7 mm and 8 mm
• Construction: forged steel
• Trivalent chrome plated per ISO 1456:2009
• Compatible with most Shimano hydraulic disc-brake bleed screws (7 mm or 8 mm by model)
• Article number: 110/1

Built in Zreče, Slovenia

Unior has been forging hand tools in Zreče since 1919, and is the official technical partner of multiple World Tour and downhill teams. The 110-series wrenches are the kind of small, forged tools that get the brand its workshop reputation: not flashy, but the flat-to-flat tolerance is right, the chrome wears clean, and the wrench doesn't deform on the third year of brake bleeds.

Pro tip from our mechanics

Bleed screws are easier to round than most cyclists realise. Two habits help: seat the wrench fully before you apply any torque, and wipe both the wrench and the screw clean before re-fitting, because contaminated brake fluid finds its way into the seal stack via the bleed port and grit on the wrench finds its way onto the screw. When the bleed reassembly moves on to the compression nut at the line end, the wrench choice changes. Bleed screws take an open-end profile; compression nuts take a flare-nut profile. The reasons live here: Choosing the right wrench for hydraulic disc brake service →