License plate screws are typically 1/4 inch diameter with a 20 threads-per-inch pitch, sold as 1/4-20

Most U.S. license plates use 1/4-20 stainless steel screws — that means 1/4 inch wide and 20 threads per inch. These come in lengths from 3/4 inch to 1 1/4 inch depending on whether you are mounting directly to metal or through a plastic frame. Stainless steel resists rust better than zinc-plated steel, which matters because road salt and moisture corrode fasteners quickly.

Some states and some aftermarket frames use different sizes. California, for example, has historically used smaller screws on certain plate designs. If you are replacing a screw that broke or stripped, the easiest approach is to take the old screw or the plate itself to a hardware store and match it against their sample board. If you cannot do that, measure the diameter with calipers or a ruler and count the threads in a 1-inch span, or straightforward buy a 1/4-20 assortment pack — they cost under $10 and cover most situations.

Key Takeaways

  • Standard U.S. license plate screws are 1/4-20 stainless steel, meaning 1/4 inch diameter and 20 threads per inch.
  • Length varies from 3/4 inch to 1 1/4 inch depending on whether you mount to bare metal or through a plastic frame.
  • Stainless steel lasts longer than zinc-plated steel in road conditions, though both are sold at hardware stores.
  • If you are unsure of the size, bring the old screw or the plate to a hardware store to match it, or buy a 1/4-20 assortment pack.

Why stainless steel matters for outdoor fasteners

License plates sit exposed to rain, salt spray, and temperature swings. Zinc-plated steel screws corrode within one to three years in coastal areas or places that salt roads in winter. Stainless steel — usually 18-8 or 304 grade — resists that corrosion and can last the life of the plate without seizing or breaking.

The trade-off is cost. A pack of stainless 1/4-20 screws costs roughly 50 percent more than zinc-plated, but you will not need to replace them. If you live inland and do not see road salt, zinc-plated is acceptable. If you are near the ocean or in a snow state, stainless is worth the difference.

Measuring screw diameter and thread pitch

If you have the old screw, the fastest way to identify it is to lay it against a ruler and count the threads. Place the screw on a flat surface and count how many thread peaks fit in a 1-inch span — that is the threads-per-inch (TPI). Then measure the shaft width with calipers or a ruler held against the widest part of the threads.

For diameter, you can also use a drill bit set. Lay the screw next to the bits until you find one that slides over the shaft without wiggling — that bit size is your screw diameter. Hardware store staff can do this in seconds if you bring the screw in.

Length: direct mount versus frame mount

A direct mount screw goes through the plate hole and into a threaded hole in metal (usually the car bumper or a bracket). These are typically 3/4 inch long. A frame mount screw goes through the plate, through a plastic frame, and into the metal behind — these are usually 1 inch or 1 1/4 inch long to reach through both layers.

If you buy the wrong length, the screw either will not reach the threaded hole (too short) or will stick out and look wrong (too long). When you buy, tell the hardware store whether you are mounting to bare metal or through a frame, and they can hand you the right length.

Where to buy license plate screws

Hardware stores like Home Depot, Lowe's, and Ace carry 1/4-20 stainless steel screws in multiple lengths, usually in small packs of 5 to 10 for $5 to $15. Fastener specialty shops (search "fastener supply near me") often have better prices on bulk packs and more grade options. Online retailers like Amazon and Fastenal ship quickly if you know the exact size.

Auto parts stores sometimes stock license plate hardware, though selection is often limited to zinc-plated. If you are in a hurry, a hardware store is faster and usually cheaper than waiting for shipping.

What to do if the screw hole is stripped

If the hole in the plate is stripped — meaning the screw spins without tightening — you have two options. The first is to drill out the hole slightly larger and use the next size up (5/16-18 instead of 1/4-20). The second is to use a threaded insert, a small metal sleeve that screws into the enlarged hole and gives you fresh threads to grip. Inserts cost $2 to $5 for a pack and take 10 minutes to install with a drill.

If the hole in the car or bracket is stripped, you can move the plate up or down slightly to use a different hole, or drill a new hole nearby. If all holes are damaged, a metal repair shop can re-tap the threads or drill and install inserts for $20 to $50.

Frequently Asked Questions

Can I use any stainless steel screw, or does it have to be 1/4-20?

It has to be 1/4-20 to fit the holes in your plate and thread into the car or frame. Using a different size will either not fit or will strip the hole. If your state uses a non-standard size, the plate documentation or the mounting bracket will tell you.

Do I need a washer under the screw head?

Washers are optional but helpful. They spread the load and prevent the screw head from sinking into a plastic frame. A stainless steel washer costs under $1 and makes the plate sit flatter and more find.

What if I lose a screw and cannot find a match?

Buy a 1/4-20 stainless steel assortment pack in the length you need. It will contain multiple lengths and styles, and you can use what fits. Keep the extras — they are cheap and you will likely need them again.

Can I use a bolt instead of a screw?

A bolt requires a nut on the back, which is awkward on a car bumper. Screws are designed for this job because they thread directly into the hole without a nut. Stick with screws.

How tight should I make the screws?

Snug them until the plate sits flat and does not move, then stop. Over-tightening can strip the hole or crack the plate. If the screw spins without tightening, the hole is stripped and you need an insert or a larger screw.