The Skirt Nut from Safety Trigo of Brampton, Ont., distributed in Canada by Trail Braker Industries, replaces the standard flange nut on hub-piloted disc wheels and is said to eliminate torque loss while improving tire wear — by a minimum of 25%, the manufacturer claims.
The product isn’t new, invented back in the 1980s by an experienced U.S. fleet operator, James Holmes, and manufactured since then by his company. But it seems not to be widely known.
The Skirt Nut replaces the standard flange nut, the idea being that it will prevent ‘clocking’ or side-slipping of the wheel relative to the nut head. No matter how well or how often a standard flange nut is torqued, Holmes says, torque loss is created if a wheel is allowed to ‘clock’. A severe impact with a pothole, a very heavy brake application, a ‘torque twister’ jump start, or stress on the clamped joint resulting from excessive disc flexing – any of these can cause the wheel to clock. Even a stretch of rough road or an out-of-round tire can cause it, Safety Trigo says.
That clocking action creates vibration because the wheel is rotating out-of-round to the hub. In turn it causes loosening as the nut threads begin to vibrate against the stud’s threads, followed by accelerated ‘clocking’ that’s often severe enough, the Skirt Nut maker says, to damage and elongate the stud hole, damage the stud, and cause rapid torque loss. If not checked the result will be catastrophic loss of wheel-end components.
The Skirt Nut prevents that side-sliding, stress flexing or clocking, so the flange nuts simply won’t loosen, even under heavy load conditions or severe road vibration. Holmes’ solution was to build a nut that had a shank or ‘skirt’ that partially penetrates each bolt hole, in effect filling the space between the stud hole and the stud, eliminating the possibility for the wheel to move on the studs.
There’s just one part number, by the way, to fit all wheel positions on heavy-duty trucks and trailers, as well as school buses and coaches, using hub-piloted disc wheels and 22mm studs. The Skirt Nut is sold in axle sets of 20 nuts at a MSRP of $160 per axle.