Wood Screw Size Chart: ANSI Gauge, Metric and Length Dimensions Table (Free PDF)

Find your gauge number in the first column, then read across for the real dimensions. Nominal Outside Diameter (OD) over thread crest is the basic major diameter, given here in millimetres, decimal inches, and shop fraction.

And those Max/Min columns is the actual factory-made allowable limits based off ASME B18.6.1. So while a #8 can legally measure anywhere from 0.157 to 0.168 in over the threads, it can vary by as much as 0.011, you’ll never get an exact read on one with a caliper.

The rolled-thread body diameter is a name given to the diameter of the unthreaded shank on a rolled-thread screw. It’s the diameter of the wire the thread was rolled from, which is as close as the standard gets to publishing a root diameter. Use this when you’re thinking about the screw’s solid core. This measurement help you judge how much steel remains at the root or check for clearance in hinge leaf.

The column labeled minimum thread depth tells you how much each flank needs to stand proud of that core. Double that and add it to your body diameter and it roughly rebuilds the major diameter.

For example, the diameter is 0.060 in plus 0.013 in times the gauge, or diameter = 0.060 in + 0.013 in x gauge, and this generates the entire second column. Observe the missing numbers in the progression. The normal sequence go from #0 to #10, then skips to #12, #14, etc., until we reaches #18, #20 and #24.

Old catalogs and restorations will also include odd numbers like #11 (which is 0.203 in), #13, and #15. But these are outside of today’s standard; consider any screw ordered in one of those gauges today as specific to that maker.

Here, threads per inch refers to the wood screw series, and a #8 wood screw is actualy 15 TPI. A sheet metal or machine screw of equal size will has different pitch, another common mistake when placing an order.

There are two kinds of traps to flag. One is that by gauge, rolled-thread and cut-thread screws of a given size don’t feel the same in your hand. A rolled screw has a diameter limited by its body, so it has a thin, even shank all through the threads. In contrast, the body of a cut screw limit its full diameter, making the tapered shank full diameter throughout. A pilot hole suitable for one is unsuitable for the other.

The second trap is that fractional label sizes at the hardware store is only approximate. Both #4 and #7 round to commonly used fractions which is off by several thousandths each. In other words, you cannot substitute a fractional-inch machine screw for a gauge-numbered wood screw in a fitted hole.

It’s the detailed ANSI ref guide to wood screws (only).

See also the Screw Gauge Chart, which shows general gauge-to-decimal conversions for all screw families. The Pilot Hole Size Chart shows the drill sizes required to pre-drill before installing any given type of screw. The Screw Size Chart provide an overview of all types of screws in one place across all families. You should of used Screw Size Chart for overview. It is moddern and helpful.

This is a sizing table where you look up the fit by the head size (not the thread). It contain details about recessed hardware and keyhole slots. It also includes information on cup and finish washers and countersunk diameter. First locate the gauge and then follow across to the column of head styles that apply to what you’re trying to fit. Everything is in inches and sourced from ANSI/ASME B18.6.1. These values are published by fastener distributors.

Heads with Equal Diameters

Both the oval and flat head diameters is equal, measured across the widest point on the 82-degree countersunk cone. With the same base they both uses one countersink setup.

The Flat Head Height Reference is how tall that cone is and how deep the head is from a flush surface. That equals depth for your countersink.

Total Oval Head Height, This is the height of the cone plus the dome on top, which shows how much an oval head will stick out once the cone is fully seated. An oval head #8 sits about .052 inches above the surface. Why? Because the cone is .100 inches tall and the total height is .152 inches.

Round heads bear on their flat underside. The height are measured from the wood surface and the footprint on the wood is the diameter.

A round head is always smaller in diameter then the same gauge flat head. In other words, a #8 round head is .309 inches while a flat head is .332 inches. Because of this difference, a cup washer that is sized to fit over a flat head will be to loose underneath a round head.

Within each gauge, each style of head share the same limit on the width of the slot. This sets the size of the flat blade driver that can fits into the slot without burring the metal.

The same heads also come as recessed heads. The standard's driver sizes determines these. Slot widths is not used for Phillips, Pozidriv, or Frearson heads.

Twice the diameter of the basic screw equals approximately the size of the flat head.

#12 screws leave a 7/16 inch diameter circle when countersunk. That’s why furniture makers don’t go bigger, they go longer.

Next time you inherit a screw hole and all you have is a countersink, how do you know what gauge it is? Simple. Divide the diameter of the countersink in half. You're right there.

This table does not apply to today's produced screws. Washer, trim and bugle-head deck screws comes in custom head shapes from each manufacturer.

The production screw table below has dimensions of both SPAX and GRK heads. Our screw gauge chart show how drivers match recessed heads. And it includes the generic diameter series of the gauges as well.

A caveat: Think of this chart as a shopping map, not a standard. You’ll find a #6 in 3/8- through 3-inches; a #12 is unlikely to be smaller than 3/4 inches. Wherever there’s a gap between what your plan requires and that range, expect a size adjustment or special-order item.

The head measures the length to where the head sits on the plane. If the head is flat or oval, the head is counted as part of the overall length, since the cone will bury into it. Then it’s measured from the tip to the top of the head.

If the head is round then it’s measured from under the head. So a 2 in round head and a 2 in flat head reach different depths. That makes a difference if you're trying not to bust through a 1-1/2 in panel.

Retail lengths take the ASME B18.6.1 increments as their stepping size within each run. This means you’ll see 1/8 in steps through 1 in; 1/4 in steps between 1 and 2-3/4 in; then 1/2 in steps after that. There is no such thing as a 1-3/8 in screw, as you can see in the #8 run: 1/2, 5/8, 3/4, 7/8, 1, 1-1/4, 1-1/2 and so forth.

The same goes with thread length. Rolled threads are at least two thirds the length, or the length of four diameters, whichever is longer. Cut threads is around two thirds of the nominal length. That’s why all long screws has a smooth shank below the head.

Why are #0 and #1 missing from the above table? They are watchmaker territory because they are stocked in lengths below 1/2 in. They are available from hobby and instrument suppliers.

#16, #18, #20 and #24 is mostly gone from general retail. Today, they exist as brass or silicon bronze in restoration and marine shops. At those diameters, the work has mostly moved to structural screws and lags. Finally, #7 and #9 are legit current sizes but many retailers bypass them. GRK builds its most popular R4 on #9, but #7 and #9 are still often skipped by stores, so treat them as bonus finds rather than plan-around sizes.

Another rule from the old shop is to choose from within a run. When screwing pieces together, place at least one gauge of side clearance from an edge and leave about two thirds of the screw in the receiving piece.

The only screw to buy in bulk would of been #8 x 1-1/4 in, which will serve as the single most useful screw for most bench work. Keep #6 x 3/4 for thin stock and #10 x 2-1/2 for frames. Here is the pilot hole size chart.

The GRK and SPAX type production screws does not follow the ANSI B18.6.1 sizing system (they use the old gauge labeling but that isn't a dimensional reference). Instead, these manufacturers list their own dimensions, and here's a table that gathers the verified numbers. The table shows the head diameter and unthreaded shank diameter. It also shows the minor root diameter of the solid core and the outside thread diameter. Finally, it lists the length range per size and the manufacturer's drive.

But the headline trap is that a production #8 is thinner then a traditional #8. On a 0.115 in shank, the #8 from SPAX is 0.163 in over the thread. The traditional #8 is 0.164 in major diameter and the body is 0.125 to 0.136 in thick.

GRK’s popular sizes are similar, running lean but their threads is sharp and deep to allow driving without pilot holes in softwood. But the strength and pull-out numbers of generic wood screw tables don’t transfer to these screws. Use the maker’s published design values. Both companies have code evaluation reports. GRK’s R4 has the ICC-ES ESR-3201 report.

The drives are proprietary, but they is actualy interchangeable.

GRK's star recess and Spax T-STAR plus both take standard Torx bits. Small GRK screws take a T15 bit, a T25 bit for GRK #9 to #12, and a T20 bit for Spax #8 to #10. A T30 bit is used on Spax #14. The Unidrive head from SPAX are driven with a #2 square driver or a #2 Phillips.

Torx type recesses transmit much more torque then the Phillips and slotted drives common to traditional screws. The reason for the recesses being able to handle more torque is so you can make the screw harder (case harden) and drive it hard into place using an impact driver without cam-out.

The work is divided by length run, but this vary with every maker. To make things easier for builders, GRK specifically bands each diameter into a range. #8 and #9 cover trim and general fastening up to about 3 in. For lengths of 2 to 4-3/4 in., it’s #10’s time. Only from that point up is there even a body on the #12, which goes from 4-3/4 in up to an almost massiv 12 in.

SPAX keeps a wider, more general-purpose spread of each diameter. Each manufacturer offer other head styles besides those pictured, such as washers, wafers, pan, and trim heads. These come in slightly different length ranges than the flat-head runs we tabulated.

Those are engineered fasteners, with case hardened threads; and they’re self-drilling (GRK Zip-Tip, SPAX 4CUT, MULTIcut). They are rated for treated lumber.

Don’t try substituting them one-for-one where an old piece of brass hardware is already in place. It’s cut for the larger shank and head dimensions shown in the tables above: those are the traditional, fatter ones. Both use root diameter for pilot drilling into hardwood; you’ll see exact drill sizes on our pilot hole size chart.

The first column of numbers is a real measurement; they're the actual outside thread diameter given in millimetres, which is how metric wood screws is sized. Reading across the row will show you the inch equivalent, which is the gauge it replaced. It will also show you the DIN 97 head geometry and so on. The variables is dk for countersunk head diameter, k for head height or countersink depth, and n for slot width.

The catalogue range of lengths lists the sizes available for any particular diameter, and as a general rule, moddern trade screws have been made longer than those ranges for many diameters. Chipboard screws from 5.0 and 6.0 mm, for instance, regularly comes in 100 mm plus.

We find the closest gauge right from the diameter. A few of these are essentially exact, like a #3 is 2.5 mm (a 0.099 inch = 2.51 mm) or a #6 is 3.5 mm or a #9 is 4.5 mm, or a #12 is 5.5 mm.

The other ones are between standard gauges, and the UK retail label column display what's sold at shops anyway. So 4.0 mm will sell as 8 gauge, though it's closer to a #7; and 3.0 mm will sell as 4 gauge. Believe the retail column if you're going by what's on packaging coming out of Europe, and believe the computed column if you care about engineering fits.

Two traps exist: (1) The conversion from imperial to metric isn't exact. A 4.0 mm screw is 0.007 in thinner than a genuine #8 (0.157 in compared to 0.164 in); that's not enough to matter on a plain clearance hole but it makes all the difference when the antique hinge has been worn down into a countersink: the metric head (7.5 mm = 0.295 in) will be noticeably smaller than the ANSI #8 flat head (max 0.332 in) and punch right through.

(2) At the high end, the retail charts don't agree. 14 gauge is marked at 6.5 mm at Screwfix; the closest you get to a #14 by arithmetic is 6.0 mm. In such a case, forget about gauge numbers completely and stick with buying by mm if the application is critical.

DIN 97 features the traditional slotted countersunk pattern, a full 82 to 90 degree cone head, a part-threaded body, and a gimlet point. DIN 95 has an oval or raised head. DIN 96 has a round head (same dia. series). This is not a good description of most metric screw available today. In reality, they are modern production or chipboard screws with Torx or Pozidriv drives.

Modern screws takes the diameters from these old ones, but differ in both thread and head form. For traditional slotted stock use this table, and the manufacturer's one above for moddern production geometry.

If one system of screws has been removed and replaced by another, you must match these three parameters: (a) the diameters shown in the table. (b) Then the head diameter, this matches the countersink. See the previous head table. (c) Finally the length in millimetres (remember, 1 mm = .03937 in).

A 1-1/4 in screw is replaced with a 30 mm screw, leaving 1.75 mm to spare. For pilot holes, see the pilot hole size chart for the correct drill sizes for metric diameter. The screw gauge chart has the complete list of metric-to-imperial diameters for every screw family.