Flare Nut Wrenches

Flare Nut Wrenches

Flare nut wrenches — also called line spanners or tube spanners — are combination wrenches with a partial opening in the ring end that allows them to be slid over a tube or hose and onto a fitting nut that cannot be approached from the end. Standard ring spanners cannot be used on tube fittings because the tube prevents them from dropping over the nut; an open-end spanner contacts only two faces and rounds flare nuts under load. The flare nut wrench solves both problems: it contacts five or six flats of the nut for maximum grip while allowing the tube to pass through the opening. AIMS Industrial supplies flare nut wrenches in metric and imperial for automotive, hydraulic, and pneumatic tube work.

Applications

Flare nut wrenches are essential for working on:

• Brake line fittings: Metric brake line nuts (10mm across flats is the most common for 3/16" and 5/16" brake pipe) corrode and are easily rounded by open-end spanners. A flare nut wrench preserves the fitting for reassembly and reduces the chance of a brake fluid leak at a damaged fitting.
• Fuel system fittings: Carburettor unions, injection fittings, and fuel line connections use the same principle — the tube prevents standard ring use and the nut is too soft for aggressive open-end leverage.
• Hydraulic and pneumatic tube fittings: Instrumentation tube fittings use compression nuts that must be tightened accurately — a flare nut wrench provides the correct contact area for controlled torque application.

Offset Versions

Offset (cranked) flare nut wrenches position the head at an angle to the handle, providing knuckle clearance and allowing the spanner to be used in tight spaces where a straight flare nut wrench would contact adjacent components. An offset version is often the practical necessity when working on in-situ brake and fuel lines.

Sets vs Individual Spanners

A flare nut spanner set covering M10 through M19 (metric) plus 3/8" to 3/4" (imperial) handles the majority of tube fitting work in automotive and industrial applications. Individual spanners in frequently used sizes — 10mm, 12mm, and 17mm are the most common in automotive work — are a useful complement to the set. For flare nut wrench recommendations for specific applications, contact our team.

Quality and Durability

The partially open ring of a flare nut wrench is inherently less strong than a closed ring spanner — quality of construction matters more than with standard spanners. A well-forged, chrome vanadium flare nut wrench maintains its shape under the torque required to crack a corroded fitting; a poor-quality tool will splay open, rounding the fitting nut and making a difficult job worse. AIMS stocks professional-grade flare nut wrenches rated for automotive and industrial tube fitting work.