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Number plate screws in Australia come in four common sizes: 10g and 12g self-tapping screws, and M5 and M6 metric screws. Self-tapping screws cut their own thread into a plastic clip or bumper. Metric screws thread into a metal nut or insert already fitted to the vehicle. The right size depends on the make, the model and whether the plate is on the front or the rear. The fastest check is to remove one existing screw and match it.

What are the four common number plate screw sizes?

Australian vehicles use two families of number plate screws. Gauge sizes (10g and 12g) are self-tapping screws that bite into plastic. Metric sizes (M5 and M6) are machine screws that need an existing metal thread. A higher gauge number means a thicker self-tapping screw, and the M number is the thread diameter in millimetres.

How do you tell which number plate screw a vehicle uses?

The quickest way to identify a number plate screw is to remove one and look at the thread. A self-tapping screw has a sharp point and a widely spaced, coarse thread. A metric machine screw has a flat or blunt end and a fine, even thread, and it only grips in a matching metal thread.

Use these checks before buying fixings for a batch of vehicles:

1. Remove one screw from the front and one from the rear, because the two often differ on the same vehicle.
2. Check the end of the screw. Pointed means 10g or 12g. Blunt means M5 or M6.
3. Test a metric screw in a known M6 nut. If it is loose, it is M5.
4. Compare a self-tapping screw against a 12g screw. If it is noticeably thinner, it is 10g.
5. Look behind the plate. A plastic plug or clip takes a self-tapping screw. A metal insert or captive nut takes a metric screw.

Which car makes use which number plate screw size?

Victoria Police published a plate screw fitting list showing the screw size used on the front and rear of common models. The examples below come from that list. It was last updated in October 2017, so newer models can differ, and matching the screw you remove is still the reliable test.

Two patterns stand out. Most Japanese makes use M6 metric screws on at least one end. Most European makes use 12g self-tapping screws at the front. Utes and 4WDs fitted with a bull bar usually take an M6 screw at the front, because the bar has pre-drilled metal holes.

How long should number plate screws be?

Number plate screws are usually short, and the safest length is the length of the screw you remove. A screw that is too long can bottom out in the clip or hit something behind the bumper. A screw that is too short will not grip once a frame or cover adds thickness.

A number plate frame or cover sits between the screw head and the plate, so it can add a few millimetres to the stack. If the original screw barely reaches through a branded number plate frame, step up one length rather than forcing it. The same applies to clear number plate covers, which sit over the face of the plate.

As a guide, common replacement kits sold in Australian hardware stores use 19mm self-tapping screws and 25mm metric bolts. Measure the screws you remove before buying in bulk for a whole fleet.

Are anti-theft number plate screws worth fitting?

Anti-theft number plate screws use a one-way or tamper-resistant head that a normal screwdriver cannot undo. They come in the same 10g, 12g, M5 and M6 sizes as standard screws, so the identification steps above still apply. Victoria Police published the fitting list above to help drivers choose the right anti-theft screw for their vehicle.

For a dealership, anti-theft screws suit used stock parked on the lot and vehicles delivered with a new frame fitted. Keep one removal tool in the workshop so the service department can still swap plates and frames.

What if you do not want to drill the vehicle or the plate?

Berlex Universal Backing Plates let a plate be mounted without drilling into the vehicle or the plate. Each backing plate is moulded from ABS plastic, adds strength to the number plate, and comes in cartons of 125 for workshop use.

A backing plate is the practical choice when a vehicle has no plate holes or the holes do not line up. It also suits customers who do not want new holes in the bumper.

Fitting branded frames across your stock

Check the screw size on each model before fitting day and keep 10g, 12g, M5 and M6 screws in the workshop. That one step stops stripped clips and second visits. Berlex makes Slimline, Standard, Premium and motorcycle number plate frames in-house in Toowoomba, Queensland, and has supplied the motor trade for over 30 years. Frames come in black or white, with a minimum order of 250 per frame type, and ship to dealerships Australia-wide. See the full car dealer range or request a quote for 250 frames on 1800 680 603.

Frequently asked questions

Why do number plate screws keep falling out?

The plastic clip or plug behind the screw has usually stripped. Replace the clip, or step up from a 10g to a 12g self-tapping screw so the thread bites into fresh plastic.

Should number plate screws be stainless steel?

Stainless steel or zinc-plated screws resist rust better than plain steel. Rusting screws leave brown streaks down the plate and frame, which looks poor on a car yard.

Can you use a metric screw where a self-tapping screw was fitted?

Not reliably. A metric screw needs a matching metal thread, so it will spin or strip in a plastic clip. Use the same type of screw that came out.

Can you drill new holes in a number plate?

Avoid drilling through the plate's characters or state name, because a plate must stay fully legible. Check your state transport authority's rules, or use a backing plate so the plate needs no new holes.