Flat Chisel

A flat chisel is the last-resort tool for stuck fasteners that have resisted every other reasonable approach. Frozen pinch-bolt nuts. A cassette lockring that has rounded all the wrench engagement points. A seatpost binder bolt with a snapped head. The job is the same: split the offending fastener with a controlled chisel strike, and recover the assembly.

The 660/6 is the 100 mm flat chisel; pocket-sized for shop work, drop-forged chrome-vanadium steel, hardened and tempered for life under hammer strikes.

What it does well

The flat-chisel geometry is the right tool for cutting through metal in a controlled direction. The chisel tip concentrates the strike energy into a narrow cutting line; the steel can then either split (a nut, a clamp ring) or shear (a bolt head, a stripped fastener). The 100 mm overall length is short enough to hold steady with one hand while you strike with the other.

Drop-forging is the construction-process choice that matters here. A chisel sees repeated shock loading at the tip and at the strike end; forged steel resists the fatigue cracking that a stamped chisel develops over time. The grain alignment from the forging step is what keeps the chisel intact across years of hammer strikes.

The chrome-vanadium alloy is hardened and tempered through the chisel body, with the tip taking the hardest treatment. The result is a chisel that holds its cutting edge through the strike and doesn't break at the strike end.

Where it earns its space in the bike shop

• Splitting a frozen pinch-bolt nut. When penetrating oil and rotational force have failed.
• Splitting a stripped cable-anchor. Where the bolt head is too rounded to grip.
• Removing a stuck headset adjustment nut. Last-resort method.
• Cutting through a stuck axle nut. When the fastener has rusted to the axle.

For any of these jobs, the chisel is the second-to-last resort. The actual last resort is replacing the fastener entirely with a new bolt and nut. Chisel work is destructive; the fastener you split is not coming back.

How to use it safely

• Wear safety glasses. The strike can throw metal chips.
• Position the chisel square against the workpiece. Off-axis strikes produce unpredictable cut lines.
• Strike with a locksmith hammer. Two-handed control on the chisel; controlled swing on the hammer.
• Keep your strike force matched to the workpiece. Soft fasteners need fewer strikes; hardened fasteners need more.
• Stop when the cut is clean. Over-striking after the fastener has split can damage surrounding components.

Specs

• Length: 100 mm
• Construction: drop-forged chrome-vanadium steel
• Hardening: hardened and tempered, tip-hardened separately
• Use: cutting through stuck fasteners as a last-resort method

Made in Slovenia, since 1919

Unior has been forging hand tools in Zreče since 1919, and is the official technical partner of multiple World Tour and downhill teams. Chisels are workshop staples in any forge-heritage tool line; the drop-forging step is the same process used on the chain tools and the BB socket tools, applied to a tool whose job is to take strike load at one end and deliver it cleanly at the other. The chrome-vanadium alloy and the targeted heat-treatment are what separate a chisel that lasts decades from one that mushrooms at the strike end after a season.

Pro tip from our mechanics

A chisel that you use once a year for the rest of your career still earns its space. The day a customer brings in a bike with a frozen seatpost binder, the chisel is the tool that recovers the assembly. For the framework on which striking tool fits which job: Hammers and striking tools in the bike shop →.