Anti Rattle Tow Hitch Shim Kit

A tow bar that rattles is a tow bar with a gap in it. These 304 stainless shims fill that gap so the tongue sits tight in the receiver instead of knocking every time you lift off. Four shims, two thicknesses, eight ways to stack them.

Will it fit mine?

The kit suits a 50x50mm box section tow bar receiver, which is the common Australian size and the one usually called a 2 inch square. Measure your receiver before ordering if you are not sure.

What it actually does

A tow bar tongue is made undersize so it will always slide into the receiver. That clearance is what knocks: every lift off, every corrugation, every set of lights. A shim takes up the clearance, so the two parts move as one instead of tapping against each other. It is a mechanical fix, not a damper, so it does not wear out or squash flat the way a rubber pad does.

Whether it goes fully silent depends on how much clearance you started with and how worn the receiver is. On a tight receiver the right stack usually kills the noise outright. On a badly worn one it will cut it down rather than remove it.

Every thickness this kit makes

Measure the play in your hitch, then build the nearest total that still slides in.

Not sure of your gap? Rock the tow bar by hand and start with the thinnest stack that stops the movement.

Why stainless, and not plated steel

Zinc plating is 5 to 12 microns of soft metal, thinner than a human hair, and the first place it wears off is the faces that rub. A shim spends its whole life being scraped in and out of a steel receiver, so a coating is the wrong kind of protection for it. Stainless has no coating to lose: scratch it, drag it in and out a hundred times, and the last surface you expose is the same alloy as the first.

The chromium in the alloy holds an oxide film about 2 to 3 nanometres thick. Gouge it off against a steel receiver and the chromium at the fresh surface takes oxygen straight back out of the air and grows a new one.

The catch, and we would rather tell you than have you find it. That repair needs air. Clamped inside the receiver, oxygen is scarce and salt can concentrate, which is the one place the film struggles to rebuild. So do what you would do anyway: hose the back of the ute after the beach, and pull the shims out now and then to let them dry.

Where we would not sell you this. If your trailer lives in salt water, 316 is the better metal and we will say so rather than take your money. 304 is the right call for a tow bar that gets splashed, dusted and rained on. It is not the right call for permanent immersion.

Near the beach it will mark. Any 304 within about 5km of surf can pick up a light brown film called tea staining. It is discolouration, it does not affect the strength or the life of the material, and it wipes back.

Specification

Care

Start with the thinnest stack that stops the movement. Too thick and it will not go in, too thin and it still knocks. Rinse after coastal or beach driving.