Machine Screw Size Chart: #0000 to 1/2 in and M1.6 to M12 Table (Free PDF)

Locate your screw size down the left column, then find it to the right for the shank diameter, followed by two common thread pitches. Gauge numbers replaces fractional screws for sizes below 1/4.

The basic major diameter is 0.060 in plus 0.013 inches per gauge number, meaning a #6 is 0.060 + (6 times 0.013) = 0.138 inches. For the three miniature sizes the formula work backward: #00 is 0.060 minus 0.013 = 0.047 inches; #000 is 0.034 inches; and #0000 is 0.021 inches.

Major Dia gives the basic diameter of the thread in both millimetres and decimal inches.

ASME B1.1 lists the two standard pitches (threads per inch) as either UNC coarse or UNF fine.

Example Callouts show how to write the size when ordering. It’s in the format of diameter, hyphen, TPI, and finally length. A #10-24 x 3/4 is a #10 diameter with a 24 TPI coarse thread and length of 3/4 in.

Look out for the onesies and the odd gaps. There's only one size without coarse thread: #0. That means there's just #0-80 UNF.

Outside the Unified system entire are the miniature sizes with NS pitches of 160, 120 and 90 or 96 TPI. You'll see those in electronics and instrument application but not in standard UNC/UNF listings.

Also, don't confuse #4-40 and #5-40, which have the same pitch but different diameters. The small screws most often confused is #6-32 and #8-32; #6-32 is 0.026 inches thinner than #8-32.

On paper you can find odd sizes like 7/16 and #12, and odd numbered gauges like #7, #9, and #11. But they aren't usually available anywere. You will mostly see designs based off even gauges and #10.

The chart for all screws doesn’t just include wood screws, there is also sheet metal screw sizes. Those follow the same system of numbered gauges, though different ranges are stocked and used according to standards.

This table is machine screw deep dive; the general screw size chart covers the cross-family overview with driver pairings. That’s all the Unified thread data that drives those pitches in the UNC and UNF thread chart.

And don’t confuse machine screw gauges with sheet metal screw gauges or wood screw gauges. It’s the same number system, but with different standards. You should of checked the chart more carefuly.

The columns shows the maximum head height (in inches) and maximum head diameter (also in inches), both according to ASME B18.6.3. Head height is measured from the top of the head to the bearing surface; diameter is measured at its greatest cross-section through the head. The height of a flat countersunk head would of been the cone depth.

There’s always some minimum manufacturing tolerance below those numbers: usually 0.01 to 0.05 in. Use these figures only as an envelope that your design will need to fit within.

Styles vary depending on how they is used. Pan head is the current general-purpose head, cylindrically sided, flat on top, seats drivers well. Flat 82° head is called a countersunk style because the finish surface is flush. Its included angle is 82 degrees (you would have to match a countersink). A column of height is the column on which this style hangs, a relative dimension depending on how sharply formed the edge is.

Round head is an older type domed over head which has been mostly replaced by the pan head. It is retained mainly for matching existing equipments.

Truss head is the shallowest of the heads but also the widest. It is useful for filling oversize slots or holes in sheet metal.

Fillister head is the deepest slotted head with the largest column height and smallest head diameter. That allow the head to be seated in a counterbore as well as handle greater torque from the driver.

The following three oddities in the standard are mentioned. 1) The 7/16 and ½ inch sizes in the row are disproportionate. The 7/16 and 1/2 in rows are not proportional because the 7/16 and 1/2 in sizes are deliberately undersized relative to the smaller sizes. There’s no flat headed 7/16 anywhere in the standard at all. Never assume that head size scales up proportionally by ratio.

The flat head diameter listed in the table above is the practical maximum, whether the edge is flat or round. Other references list the theoretical sharp corner head dia which is approximately 6% larger. For example: a #4 flat head is 0.212 in actual but 0.225 in to the theoretical sharp corner. Use this table if checking a screw with calipers. Use the theoretical value when sizing countersink.

3) Though the standard does list miniature #0000, #00 heads, they’re available only in a few styles and from certain suppliers.

Before specifying over a slot, be sure to examine the truss column for fastener choice. A #10 truss covers a 7/16 in hole. Also note if the screw goes into a counterbored hole (counterbore height).

This table does not include oval heads, hex heads, or washer heads. Those are covered in another table (below).

It’s worth noting that oval head is simply a flat 82° head with an added round top, so its diameter matches the flat column. Slotted, Phillips, and combination drivers all use the same head dimension. The corresponding driver sizes for those heads is listed on the general screw size chart.

Drill designations includes number, letter, and fractional sizes with decimal inch equivalents in parentheses.

Clearance columns occurs when a screw goes through a part without cutting threads inside it.

The clearance drills give a close fit allowing for accurate location of parts with snug hole. They also allow for some working room for general assembly and for paint or plating build up.

Tap drill columns is used for cutting internal screw threads.

Here you simply drill the column size given and then go back in with the appropriate UNC or UNF tap to cut the thread. The drills is around 75% thread engagement, which is standard for materials like aluminum, brass, mild steel, and plastics, but you should of drop to 50% for hard or tough materials.

For a couple of sizes there is disagreement among published tap drill charts by one size drill number. Engagement percentage targeted vary among chart makers. For example you will find #39 instead of #38 for #5-40 and #51 instead of #50 for #2-56. You’ll find #17 different than #16 for #12-24. And any of those will give a working thread.

The figures here are based off the popular 75 percent machinist chart. In tough or hard material (work hardening alloys, cast iron, stainless) drop down to a 50 percent thread drill. The tap run much easier and doesn’t lose strength. On that separate tap drill chart are metric sizes, deeper engagement options, and forming-taps data.

Here are some typical clearances called out as pairs: Close and Free. Those are the old machinist close & free fits. They are about 0.003 to 0.016 in oversize from the screw diameter.

Clearance holes are formally defined in an ASME B18.2.8 system using close, normal, and loose categories. Slightly different drills, and those names. A close fit #6 is #23 on the B18.2.8 system; #27 on the traditional chart, for instance.

Pick one system (like traditional or ASME) and stick with it throughout your drawings.

The clearance hole chart also includes countersinking and counter boring sizes to allow head screws to sit flush.

No standard clearance drills, but they does take tap drills on the three miniature sizes. #0000-160, 1/64 drill. #000-120, #71 drill. #00-90, #65 drill. These are all essentially the same as the minor diameter of the threads.

Shank is 0.021 to 0.047 in. Drill a fraction more than that for through holes. At this scale taps snap easyaly.

Use a lubricant and peck-tap by hand. First check engagement on scrap. For each size in the table, drill perpendicularly. Guide block or drill press beats freehand. Deburr before tapping, any burr on the entry throws the tap out of alignment.

The regular hex A/F column display the nominal width across the flats. You use it for your wrench or nut driver. The A/F min and A/F max values is the manufacturing limits on that width.

Head height are the distance from the top of the head down to its bearing surface.

Five sizes offer an option for a larger head as defined by ASME B18.6.3. It’s primarily for SEMS (screw-and-washer assembly) applications where the washer require more bearing surface. These heads is lower than their counterparts from the regular pattern.

On many screws, the size of the wrench repeat for other sizes. For example, number 3 through number 5 screws has a 3/16 in hex. And number 1 and number 2 screws has a 1/8 in hex. Number 6 and number 8 screws has a 1/4 in hex. And number 10 and number 12 screws has a 5/16 in hex.

You can’t tell which thread the wrench is from just by looking at the wrench. So look to see what the diameter is, or how many threads there is per inch before ordering replacements.

For example, a 1/4 in hex washer head sheet metal screw has a 1/4 in driver like a common #6 hex head machine screw. This is another potential easy mix-up in the parts bin.

Hex machine screw heads is shorter and slightly smaller than hex cap screw and bolt heads of the same thread: Hex cap screw and bolt head dimensions (e.g., ASME B18.2.1) is bigger and taller than those of hex machine screw heads of equal thread size. For instance, a 1/4-20 hex cap screw’s head is 7/16 in A/F; a 1/4-20 machine screw’s head is 3/8 in A/F and roughly 0.19 in tall.

Don’t take your head dimensions from a bolt chart for the machine screws. By default their heads are plain, and they’re driven solely with a socket or wrench. Optional top styles include slotted tops, cross-recessed (Phillips) tops and ones with an indentation in the middle. All trim styles follows the height and across-flats limits shown in the table.

For hex head machine screws, their standard run are up to 3/8 in; beyond that it’s into hex cap screw and tap bolt territory.

For washer heads and serrated flanges, those are not B18.6.3 items but manufacturer specials. If you require one of these, check with the maker for dimension confirmation via their drawing.

The socket and spanner wrench size chart is here for wrenches compatible with these A/F sizes.

The left-hand column give you the thread size. The next one is the coarse pitch (millimeters per turn of the threads per ISO 262). Next are the pan head envelope, the countersunk head envelope and the workshop drill sizes.

These are the two workshop drills that will fit the fastener's hole. The pan head envelopes is called Pan dk and Pan k. This is the max head height and diameter for a ISO 7045 cross-recessed pan head.

For the countersunk head, Csk dk sharp is the diameter up to the theoretical sharp corner according to ISO 7046-1. Then there's Csk dk actual, which is the true max at the rounded edge on the finished screw. And finally there's Csk k, the countersink depth.

Countersunk machine screws with metric threads has a 90-degree included angle. Those with imperial threads have 82 degrees. What does this mean? It means that imperial countersinks sits the metric flat heads proud.

The actual diameter, as measured by calipers on your screw, is different from the sharp diameter, as modeled in CAD or used to choose a countersink. Getting these confused causes an M4 head to appear 1 mm too small.

The clearance hole is the ISO 273 medium series through-hole, which is a convenience value. The tap drill column show the major diameter minus pitch. This is the standard drill for roughly 75 percent engagement. The tap drill chart shows fine pitches. There are also forming taps. And engagement options. The clearance hole chart includes fine and coarse series. Counterbores

Metric machine screws has the big trap of DIN vs ISO head dimensions. Two ISO head sizes (M3 and M5) differs between DIN 7985 old pattern pan heads and ISO 7045. For M3 it's 6.0 mm under DIN vs 5.6 mm under ISO. The same applies to M5: it is 10.0 mm under DIN versus 9.5 mm under ISO.

From M3.5 up ISO 7046-1 countersunk heads differs, being larger than DIN 965. An M4 DIN 965 is 7.5 mm actual vs 8.4 mm for ISO. An M8 is 14.5 mm vs 15.8 mm.

In this table, much of Europe stocks the ISO dimensions today. But older bins and drawings still mix both. Measure before you countersink. Note that M3.5 is not a preferred size per the ISO standards and so is bracketed as such. Best should of avoid using in new designs.

M10 is the last standard head size

ISO 262 coarse pitch of 1.75 mm remains in place with M12.

M12 keeps its ISO 262 coarse pitch and drill sizes

However, there’s no standardization of cross recessed pan or countersunk heads on that diameter. For that diameter you will specify a hex head to ISO 4017. Or use a socket cap to ISO 4762. Or use socket countersunk to ISO 10642. You can also use Torx pan variants.

Raised countersunk heads to ISO 7047 shares the same diameters as ISO 7046-1. With a domed top added.

The general screw size chart shows which driver pairs go together, Phillips and Pozidriv, using this metric system. This table continues the dimenional depth.