Screw Size Chart: Imperial and Metric Screw Dimensions Table (Free PDF)

To use, go down the first column to find your gauge number, then across to read off the shank diameters in both decimal inches and millimetres. Also shown is the two most common head styles, their maximum width, and a Phillips driver typicaly used. That’s the entire imperial run ID table.

Go down the Major dia columns if you have a screw whose diameter you can caliper across its threads; those gives you the gauge. Then the head columns verify.

Major diameter is the outside diameter measured over the crest of the threads. This measurement apply to sheet metal, wood, or machine screws of this gauge. For imperial they goes by the following formula: 0.060 in + 0.013 in per gauge number. Thus #6 is 0.138 in and #10 is 0.190 in.

The pan head diameter is the maximum head diameter for pan head machine screw per ASME B18.6.3.

The flat head diameter is the maximum actual diameter for 82 degree countersunk machine screws from the same standard.

Phillips driver: The recess number matches the standard pairs for that size in common head styles.

Only #7, #9, and #14 in the list lack pan head cells. This is because they exist only as wood and tapping screw sizes.

Machine screws skips from #6 to #8, #8 to #10, etc., and from #12 to 1/4. The ANSI B18.6.1 wood screw standard provides the flat head values for gauges #7, #9, and #14, while machine screw flat head values comes from ASME B18.6.3. These are theoretical sharp values, so a real head measures slightly smaller; the machine screw flat head diameters listed here are the actual maxima you'll measure with calipers.

Here the flat head diameters are actual maximums, the measurement you would get if you used calipers across the top of the head. Catalogues sometimes print the larger theoretical sharp diameter instead. Sometimes you'll find two flat heads with the same number but different printed diameters, such as 0.312 in and 0.332 in for a #8. These are actualy the same screw.

Flat head size says what size the countersink should of be to make the screw flush. So if the diameter of the flat head is .31 inches, that’s the size the counter sink should be.

Pan head diameter shows you how big the bearing surface of the screw is. And if you get some hardware that already has holes drilled in it, you can measure the recess and match it to the Flat head dia column to pick out the correct gauge.

The table intentionally ends at heads and diameter. For more detail about threads per inch, use the screw gauge chart. That also covers coarse vs. fine series.

Those are further discussed in the machine screw size chart, wood screw size chart, and sheet metal screw size chart. There is even a separate chart of pilot hole sizes.

You get into bolt territory above 3/8 in. Lag screws and cap screws uses different standards for heads. They are not in the table here.

They call Metric screws by their major diameter in millimeter units. An M5 have a thread crest width of 5.0 mm. The first two columns merely repeat this in each system of units.

The next column is the pitch of the threads, which is coarse for almost all the metric screws below M12 that we stock. The head diameter is then listed for the two standard cross recessed patterns. Finally, the table indicate the recess number for each type of driver: pozidrive (type Z) and Phillips (type H).

Pitch, the space between successive threads, coarse, Pitch included in the screw's size designation (diameter x pitch), Almost all stocked metric screws below M12 is coarse.

The pan head diameter is the maximum head diameter per ISO 7045., Standard cross recessed pan head screw.

Csk head dia is the maximum actual head diameter for countersunk flat heads per ISO 7046-1. This is measured across the top of an actual head. The theoretical sharp diameter used to size countersinks is larger. The actual size is 8.4 mm on M4.

PH / PZ driver, Number of cross recess assigned by ISO standards to that size. The number is the same for both recess types.

Where metric trips people up most, though, is that there's also an overlap between legacy DIN and ISO standards. For instance, DIN 7985 pan heads match a PH1 recess with an M2 size while ISO 7045 matches a PH0 recess with an M2 size.

On M3 size, DIN gives it a 6.0 mm head; M5 gets a 10.0 mm head. Under ISO standards, those same sizes are 5.6 mm and 9.5 mm. On older DIN 965 countersunk heads they're even smaller. M4 size has a 7.5 mm head, M8 is 14.5 mm. Those would of been 8.4 mm and 15.8 mm respectively.

Both types of screws continue to be sold alongside each other. If you have a replacement head that seems a little off in one of your old countersink, chances are you're straddling DIN and ISO. You didn't read it wrong.

Most suppliers does not stock M3.5 very well.

M3.5 is their equivalent (metric) to the imperial #6 screw. They mostly survive in electrical fittings, switch plates and some appliance work. Skip from M3 to M4 if you’re designing instead of fixing.

M12, This finishes out the common sizes; included here even though cross recessed heads stop at M10.

Cross recessed heads top out at M10. Anything larger uses hex, socket, or Torx heads. Those are covered by different head standards.

This is a table of screw sizes and drivers, and if you have a metric screw, select one from the table above.

Thread charts and machine screw size chart contains tap drill sizes, thread tolerances, and even fine pitch series. Related ISO standards contains head heights, property classes, and full recess penetration data.

The values in this chart are for the two styles you’ll see in the hardware aisle, pan and countersunk.

This table helps you respond to the two most common questions about screw length, which are the ones that get returned most often. Where does the stated length come from? And what’s on the shelf?

Locate your screw type in the left hand column. Then look at how it is counted for length. Finally read down the relevant diameter and length columns to find out what is actualy available to buy.

To measure length, simply look at where the head sits on your surface. Trim, bugle, and flat countersunk heads will be included in the listed length if they sits beneath or flush with the surface. If the head is designed to sit proud of the surface, then the measurement is taken from underneath the head up to the tip.

This would apply to washers, hex, buttons, truss, pan, and round heads. Oval heads take the middle road. Measure them from their widest bearing points on the head.

When self drilling screws is used, include the drill point in the length. The point won’t bite into the material.

Pan head screws, at 25 mm long, go further below the surface then a 25 mm long countersunk screw. The pan head goes all the way through, but the countersunk ones don't go as deep as their length suggests.

What you see in catalogs, what is carried by retailers, is typical of what is stocked. It is not the limit of the standard. Metric woodscrews range from 12 mm through to 300 mm. US wood screws range from 3/8 in through to 6 in. Plasterboard screws go up to about 100 mm.

Above this, go for timber screws as they are better. Machine screws is short. Stock generally is below 35 mm. Above this it's mostly 1/4 in and up or M6 and up.

In the Size callout example column, you can see how they’re marked on the box, one per family. Diameter x length for metric woodscrews. (A 4 x 40 mm screw is 4 mm dia., 40 mm long.) Gauge x length for US wood screws. (#8 x 1-1/4 in = number 8 gauge, 1-1/4 in long).

Add the pitch if it’s a machine screw. (M4 x 0.7 x 16 means the screw includes the pitch.) For metric machine screws with just two numbers on the box, the pitch is the default: coarse.

Torx size printed on box, as more deck screws & structural screws do; check vs. The driver pairing table is below.

Length: For that reason, you select based off desired engagement with the material. With screws intended for plate or sheet work, you engage the entire depth of tapped thread or nut. With those for wood, you get about two-thirds of the screw in the base material.

To account for screw not breaking through, take off the head allowance. For that you should of rely on the measurement rule above. Pan vs Flat heads is important here.

Partially threaded screws are not accounted for in this table. It varies by family. These are covered in the chart for structural and wood screws.

The first two columns list the screw size; match it up to the driver size in whichever drive family the screw carries. These combinations shrink the typical size chart down to one row per size. This includes Pozidriv and Phillips numbers from the ISO and ASME recess tables, Robertson square sizes with the usual handle color codes, and the Torx sizes most often found on flat head and pan head screws of that diameter.

There’s a whole range of sizes. Phillips goes from PH0 to PH4. Within that range a single driver is used for a wide range of sizes. For instance, PH2 fit both #5 through #10 machine screws and both M3.5 through M5 screws. So he is found in all drill cases.

The only messy row is the #10 row. #10 machine screws fit PH2, while #10 and up (wood) screws are cut for PH3.

Pozidriv numbers match the Phillips numbers size-for-size. But the recesses is not interchangeable. Pozidriv heads are marked with tick lines between the cross arms. If you see those, you should of swap bits because a Phillips bit will not sit correctly in a Pozidriv and will slip under torque.

By convention, Robertson square sizes is color coded on the driver handle. Orange is #00 for the smallest gauges, yellow is #0 for #3 and #4, green is #1 for #5 to #7, red is #2 for #8 to #10, black is #3 for #12 and 1/4 in, and brown is #4 for anything bigger then that. PH2 is usually considered part of every day’s territory and red #2 covers the same ground.

Because the amount of metal around a head varies depending on its design, heads has different sized recesses and are paired with specific torx sizes based off the head style. For example, a #8 flat head take T15 against a T20 pan head. Socket cap screws are larger still and their coverage is also listed in the torx size chart.

The Torx columns are typical. However, not all companies use the same head shape. Each chooses their own for their branded structural and deck screws. Although you might think the gauge calls out T20, most new decking uses T25 regardless. Always check the tech sheet or, better yet, read the packaging to see what's in the box.

Where there is a blank cell, it indicates there isn't a common pairing. It is not because it can't be done, just because it's uncommon.

For example, you want to identify a mystery screw, so you use the pairing in reverse. A snug fit with the PH2 bit mean the screw is roughly M3.5 to M5, or #5 to #10. That narrows the calipers work considerabley.

The specific hex key size chart and Torx size chart show the full depth dimensions of every drive system. The charts show you torque capacities, recess depths and tip widths. This table only answer which driver to pick up for a given screw.

Use this table as a guide if you are trying to substitute between systems (e.g., purchase tapping screws, wood, chipboard) and want to know what's closest in metric.

The Difference column has a sign that tells you how the two diameters compares: Positive? The metric screw is bigger, fatter. Negative? The metric screw is smaller, slimmer.

It’s written again in mm with Dia (in / mm), so you can see it at a glance if you are comparing to the imperial table above. The Nearest metric column is the one actualy used in the trade.

It’s also how European, UK, and other retailers sells mixed stock of these sizes, the workhorses. So they sell gauge 6 as 3.5 mm. They sell gauge 8 as 4 mm. Gauge 10 as 5 mm. And gauge 12 as 5.5 mm. The Watch out column flags up what the raw difference number mean in practice for that pair.

It's not how much of a difference but what direction the difference goes. If the metric screw is slimmer, an existing hole drilled for the US screw will be slightly loose, but it should still work fine in wood.

If the metric screw is fatter (e.g. M3 vs #4 or M5 vs #10) then you need to pre-drill pilot and clearance hole for the metric screw. Otherwise the screw will get stuck and may split.

#3 and M2.5 are nearly perfect twins, you can swap them back and forth freely in wood. #6 sells as 3.5 mm. The two near-perfect twins, #3 with M2.5 and #6 with M3.5, swap freely in timber. But M5.5 isn't a common size at all; most suppliers don't even carry it in stock.

Bolt and machine screws does not intermingle systems.

A #10-32 and an M5 x 0.8 are close in diameter, but their threads will strip each other if forced; 1/4-20 against M6 x 1 is the same trap one size up.

If it’s a screw mating with a tapped hole, insert or even a nut, get the system the female thread was cut in. This table shows screws cutting their own thread in sheet material or wood.

Pay extra attention to these two rows: #14 and 1/4 in. You might look at them and think they’re interchangeable, since the 1/4 in is the next machine screw size after the #12. But then you realize that a #14 wood screw isn’t 0.250 in; it’s 0.242 in. That means the pair maps to M6 (both slightly fatter than the M6, hence the minus signs).

The entry for 3/8 to M10? It’s there because it’s the closest neighbor, not because it’s a close fit. They’re almost a half millimeter off. Heads, holes, countersinks, they don’t agree either. Consider these separate screws that just happen to be neighbors.