45.2mm Australia Grommet Dust Cap (Pair)

$15.84 inc GST

or 4 fortnightly payments of $3.96 with Afterpay More info

SKU: CM495 Category:


Last updated on January 11th, 2020 at 12:22 pm

45.2mm Australia Grommet Dust Cap. Fit all standard trailer hubs (45.2mm).

How do dust cap grommets work?

A rubber grommet that expands and contracts during normal driving conditions.

The air chamber in hub expands when in highway mode and contract when immersed in water.

It is common to fit hubs with grease and then experience grease overflow on the inside of your wheel hub.

Have dust cap grommets been used before?

Grommet Dust Cap have been commonplace in the USA for decades and standard on most US boat trailers.

Tested and Patented

Couplemate have an Australian Patent on this 45.2mm Australia Grommet Dust Cap.

Boat Trailer bearings have been a problem for a long time and continue to be a problem for many boat owners.

Bearings are not only a problem for boat owners but Caravan owners with bearings due to high-speed, highway usage.

Worn bearings and even damaged stub axle journals are a result of water ingress into the bearing cavity.

Water entry into hubs is generally through the back seal and is a common boaties problem.

However, if the lip of the marine seal is not greased during insertion then seal failure is common.

I need a better marine seal, yes that is a FURPHY.

I am sorry to say this, and I understand countless hours are spent on public education, however marine seals are useless unless the lip is greased prior to insertion.

Current Australian and US marketing say use Bearing Protectors and then pressurise your hub to 3 psi.

You will not get water ingress because the tension in the bearing protector spring will counteract the contraction in the cavity due to cold water immersion. That is also a FURPHY.

Pressurising bearing protectors at three psi in a cold hub only results in that pressure being released on the highway when the hub is hot.

Have you noticed the grease marks on the inside of your wheel? Impossible to remove?

As the hub gets hot, the air within expands, remember that spring was under full tension at three psi when cold?

Now the expanded grease isn’t going back inside the bearing protector or bearing buddy because the bearing buddy is already loaded and under full tension, since there is nowhere for the grease to escape except through the back seal.

WALLA, grease over the inside of our trailer hub.

As the hub grease gets hot and fluid, the grease in the bearing protector will escape into the bearing cavity and then out through the back seal?


There is a lot of talk from experts about putting Chinese quality bearings into your boat trailer, and THAT IS the remedy for failed bearings. Another FURPHY.

Indeed, poorer quality bearings FAIL earlier, but it is generally not the root cause of boaties bearing problems.

Another Prime cause of bearing failure is pumping good grease ON TOP OF BAD GREASE?

If you have BAD grease, remove this rancid grease, and bearings checked for wear.

Contaminated grease can be light tan colour or black grease; tan coloured grease usually indicated water contamination.

Black grease may be carbon steel deposits in the grease from bearing and axle wear.

What happens during water Ingress and Badly Install Seals

Bearing failure due to WATER INGRESS is the root cause of a boaties bearing problem, and it’s now a thing of the PAST for most boat owners.

Couplemate has found the science to the BEARING FAILURE SOLUTION

Couplemate discovered that putting a hot trailer hub into cold water causes the air inside the hub to contract.

This contraction causes water to be sucked in through the back seal. Simple as that.

After years of testing, water generally enters the hub through the marine seal and more precisely water enters around the outside of the marine seal. (given there is no wear on the bearing journal)

Couplemate inserted a rubber diaphragm on the outside of the dust cap (or rubber grommet). The rubber grommet is pushed out as Air Expands and then is sucked into the bearing cavity when contraction occurs. It is the rubber grommet that expands and contracts due to dramatic changes in air temperature.

Boaties still check their wheels and apply regular maintenance, but they are not buying bearings.

Bearing failure is being minimised in the Australian market for boaties using Couple-mate Premium Dust Covers. Grommet dust covers are standard equipment on American trailers, especially boat trailers.

Couplemate have produced a set of dies to suit Australian hubs and created a stainless Grommet dust cover.

Purchase similar grommet dust caps here:

45.2mm Australia Grommet Dust Cap

Couplemate Trailer Parts sells only the best quality 45.2mm Australia Grommet Dust Cap (Pair) and caravan spare parts throughout Australia. Customers are welcome to either pickup or take advantage of our low freight rates. Express shipping to Melbourne, Sydney, Brisbane, Perth, Adelaide, Darwin, and Hobart. We also ship products to New Zealand via Australia Post Air Express.

Additional information

Weight 0.4 kg
Dimensions 20 × 6 × 6 cm
Plain or Galvanised

Plain K1045 Steel, Galvanised + $15.00


There are no reviews yet.

Be the first to review “45.2mm Australia Grommet Dust Cap (Pair)”