AN Wrenches

AN wrenches are aluminium spanners sized to the hex nuts and fittings of AN hose ends and adaptors, so they can be tightened without chipping or rounding them. The range runs from AN4 to AN16, alongside a universal adjustable wrench.

AN fittings, a standard taken from aviation, seal metal to metal on a 37° flare rather than on the thread. The thread only draws the flare together, so the joint needs moderate force, and too much distorts the flare or cracks the nut. The fittings are usually anodised aluminium, which a steel spanner marks and rounds, while an aluminium jaw spreads the load over the flats.

The dash number counts sixteenths of an inch, so AN6 matches 3/8 in tube. Pick the wrench by the dash size on the fitting:

• Size: AN4, AN6, AN8, AN10, AN12 and AN16, from small oil feeds up to large oil and coolant lines.
• Colour: listed in black, red, blue and yellow, which makes sizes quicker to tell apart in a tool tray.
• Adjustable wrench: for other hex sizes, or to hold an adaptor while the nut is turned.

Hold the adaptor or hose-end body with one wrench while turning the nut with another, so no twist passes into the hose or the part it is screwed into. Lubricate the threads and flare with a little clean oil, or brake fluid on a brake line, to prevent aluminium galling.

Tighten by hand until the flare seats, then add a small turn with the wrench rather than heaving on it. Check every joint for seepage after the first run and heat cycle. Keep the wrenches for AN work, as their soft jaws wear quickly on steel fasteners.