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Screw grommets: what they do and how to size them

3 min read · Clip types explained

A screw grommet is a small nylon insert that pushes into a hole in a panel. When a self-tapping screw is driven through it, the grommet spreads behind the panel and the screw has something solid to bite into. They are used where the panel has no thread of its own.

Where you will find them

• Number plates and number plate brackets
• Inner guard liners and mud flaps
• Grilles and bumper parts
• Under-trays and splash shields

Sizing a grommet

1. Hole shape and size: many grommets are square, some are round.
2. Body length: long enough to pass through the panel and spread behind it.
3. Flange size: the head that sits on the front of the panel.
4. Screw size: the centre hole suits a certain screw gauge.

Our screw grommets pages list the flange, body and centre hole sizes shown on each photo. See how to measure a car clip for where to measure.

Fitting tips

Push the grommet fully into the hole first, then drive the screw. Stop when the screw is snug; over-tightening strips the nylon. If an old grommet has split, replace it rather than using a bigger screw.

Related parts

Screws to suit: automotive screws. For clips on a panel edge: speed clips and speed clips explained.

Square or round?

The grommet must match the shape of the hole. A square grommet in a square hole cannot spin when the screw is driven, which is why many cars use square holes for number plates and liners. A round grommet suits a round hole. Using a round grommet in a square hole, or the other way round, usually means it spins or does not hold.

How to remove an old grommet

1. Undo the screw. If it spins without coming out, pull gently on the part while turning.
2. Squeeze the grommet from behind the panel if you can reach it, then push it out.
3. If it is stuck, cut the flange with a sharp blade and push the body through.
4. Clean the hole before fitting the new one.

Common mistakes

• Using a bigger screw in a worn grommet. It may hold for a while but will split the panel or grommet later.
• Choosing a grommet that is too short for a thick panel, so it cannot spread behind it.
• Driving the screw at an angle, which tears the nylon.
• Using power tools on full speed. Finish by hand.

Screw grommets: sizes in our range

We measured the screw grommets in our own range from the marks on each product photo. Of 2 products with sizes, the stem (which roughly matches the hole size) runs from about 9 mm to 9.2 mm. The most common stem sizes, rounded, are 9 mm. Here is a spread across the range:

Sizes are approximate, read from the measurement marks on our product photos. Always compare with your original part.

Frequently asked questions

Are screw grommets the same as plastic nuts?

Yes, many people call them plastic nuts or screw inserts.

Can I use a screw grommet in a round hole?

Use a round grommet in a round hole. A square grommet in a round hole will spin.

Sizes and fitting steps in our guides are general. Check your vehicle's manual for anything specific to your car. Questions? Call 0499 001004.