Washer Size Chart: Flat & Lock Washer Table (Free PDF)

Read the row from left to right. Find your bolt size in the first column and then follow that row across. Nominal outside diameter is called out as OD d2 (mm). Nominal clearance hole through the washer is called out as ID d1 (mm). Nominal thickness is called out as Thickness s (mm).

Then we have the tolerance columns which provide the limits of what a standard washer might actualy be. Hole size max, or ID max would be the biggest hole that is permitted. Outside diameter min is the smallest outside diameter permitted. Thickness min - max is the allowed band of thickness. So even though it doesn't match the nominal number, if you take a caliper reading inside these bands, it is in spec.

The ISO 7089 standard is for the metric normal series.

This is the standard washer, the one that goes underneath the head of a metric hex nut or bolt. It replaces the old DIN 125A. These two washers is dimensionally equivalent at each size in the table above. So if you have stock marked as DIN 125A, it will fit anywhere that an ISO 7089 is specified.

The ID of the washer is always slightly oversized to accommodate the bolt. So an M10 washer has an ID of 10.5 mm and will drop down onto a 10 mm bolt with adequate clearance.

Is it a washer that says M10 but is only 10.0 mm across the hole? That’s not an M10 washer. That’s either an M9 or someone made a mistake on the label.

Before reusing a washer beneath a high grade bolt, you should of check the hardness class. Property classes through 8.8 are ISO 7089 at 200 HV. Bolts with a property class of 10.9 and socket head cap screws are 300 HV.

A 10.9 bolt being torqued down onto a soft 200 HV washer embeds into it. Within hours, the joint has lost its preload. These two classes appear identical. If the box doesn’t say 300 HV, you assume it isn't.

You may be interested in two close misses. One is that there’s an ISO 7090 washer with just the right sizes from the table except it has a chamfer on one side. This is because of big fillets underneath bolts. The chamfer should point toward the bolt head.

The other is that some manufacturers still stock pre-ISO DIN 125 large washers, which have a smaller hole and thinner section. From M39 upward they has a smaller hole. So for example, M39 was 40 mm rather than 42 mm. M42 was 43 mm rather than 45 mm. They were also thinner in section. Always check what standard the box cites for sizes above M36.

So this table doesn't include structural bolt assemblies, which use a thicker, harder washer like EN 14399-5/6. It also excludes the smaller OD ISO 7092 series below socket head cap screw. It also does not include the larger OD fender series below that we'll cover later on this page.

The left-most column indicates the size of the screw or bolt you want. Then pick a series from there. The three SAE columns gives dimensions for the narrow pattern, and the three USS columns gives dimensions for the wide pattern. Each set includes the inside diameter, outside diameter, and thickness for Type A narrow (narrow pattern). It also includes those same measurements for Type A wide (wide pattern). These numbers is given in basic inches.

The dash indicates that series isn't defined by the standard for that size. For sizes smaller than 1/4 in, the narrow pattern is all that's made and sold as SAE. For sizes larger than 1-1/2 in, it's the wide pattern and it's sold as USS.

What’s practical? Fit and bearing area. For a 1/2 in bolt, a USS washer is 1.375 in across with a loose hole of 0.562 in. An SAE washer is 1.062 in across. The SAE has a smaller outside diameter and tighter inside diameter, that makes it suitable for automotive and machinery work. Its small diameter fits narrow flanges and counterbores.

USS is the larger, looser washer of the two. If you only have one rule to go by, make that one: use USS for timber and construction. Its large footprint spreads out the load on oversized or soft hole.

ASME basic decimals are what these numbers are; they’re what a measuring caliper should of approximately agree with. In retail listings, they’ll typically be rounded to fractions. A 0.734 in basic OD USS 1/4 in washer has a 0.312 in hole (sold as 5/16 in) and it’s listed as 3/4 in OD. They both describe the same part.

There are wide thickness tolerances: a nominal 0.065 in washer can legal be between 0.051 and 0.080 in. Because of this variation, never use stacked flat washer as precision spacers.

Don’t mix the series within a single joint line. Using an SAE washer under the nut and a USS washer under the head create unequal pressure at both ends of the bolt. This causes the joint to relax unevenly.

Moreover, even though those unhardened washers might provide some benefit, they’re not a substitute for a structural washer. Hardened ASTM F436 washers is necessary because high strength bolting is required to work per A325/A490 and F3125 standards. Those hardened washers has similar diameters, but they are tighter in tolerance and through-hardened.

#2 to #12 are machine screw sizes. To find the inch diameter, use the formula 0.060 + 0.013 x the number. A #10 screw is then 0.190 in.

Skip this whole series if you have soft material or drilled an oversized hole. Instead go to the fender washer table below.

Now follow down the table, finding your thread size. Read across. The Section thickness s(mm) are the axial thickness of the square wire section. The Section width b(mm) is its radial width.

The d2 max (OD mm) is the largest flattened outside diameter. The d1 min (ID mm) is the smallest hole a washer of this size can have which will always clear the bolt. The H (Free height mm) is the height at which the open helix stand prior to being tightened. The washer is one section thickness s tall when completely compressed.

The classic split washer is DIN 127 form B, which have smooth ends on a square section washer. Sharp ended (tanged) is form A.

The D2 is the maximum value. It's a helical ring. As you crush it flat it will grows a fraction and the flattened diameter will vary very slight across its length. This means that if you're measuring inside a counterbore for clearance you'll add margin to d2 max.

Here’s the truth: A fully torqued split washer is just flat. Some fastener manufacturers has demonstrated this through testing. What little locking action it have over a plain washer isn’t worth it.

DIN itself withdrew the standard. DIN 25201 for railway applications specificly excludes split washers as a locking element.

On small screws, sheet metal covers, grounding lugs and other low-preload joints, they makes some sense, since the sharp edges bite there. On legacy equipment where the drawing calls for them, of course they make sense too. But for critical vibration joints, you pick something else: serrated flange bolts, prevailing-torque nuts, wedge lock washers, adhesives.

There is two usage traps. Never use a soft flat washer over top of a split washer. It loses the bite and the spring act on the wrong side. And you never reuse a fully flattened split washer, it loses its springiness once it is set.

Grade 10.9 and 12.9 bolts also has their weak point at the washer. The bolt gets to preload, but the edges of the washer gouge into the seat.

The standard covers a single wire section for sizes M68 through M100 (14 x 8 mm). If you want something bigger than an M64, you’re likely looking at special order because these are hardly ever available off-the-shelf.

This table doesn’t include conical disc washers (DIN 6796), wave washers (DIN 137) or curved spring washers (DIN 128). They are different pieces of hardware that does different things.

The first column shows your screw or bolt size and you read across the row for its specs. Nominal thread diameter is shown in parenthesis as a decimal. Hole permitted limits is shown as ID min and ID max. The OD max is the flattened outside diameter size limit.

Wire section thickness are an average of the whole wire section, mean section thickness. Because it is very slighty trapezoidal, the standard takes the inside and outside edges and averages them. Radial section width minimum is the narrowest part of that section radially.

The regular series is what most catalogs and hardware stores mean by a spring or plain split lock washer; see ASME B18.21.1. It has the same ID but narrower and thinner sections. Heavy and extra duty series also use the same IDs but have thicker and wider sections.

Your washer might be noticeable fatter than what is in the table: it is one of those series, not out of spec. A regular washer's free height will be about two times its section thickness, so account for that much more thickness as grip length when adding one to a stack-up.

Be careful with the washer choice versus the joint hardware. Under a hex head, the OD max column tell you whether the washer hides under the head or sticks out. A 1/4 in regular series washer is 0.487 in across and protrudes on small hardware, but a 1/4 in hex head screw is only 0.438 in across the flats.

Regular series will not normally fit in a counterbore for a socket head cap screw. For that situation there is the hi-collar series which is not shown in the table.

The same locking caveat applies to the metric table. Although a compressed split washer add little security at full preload, many manufacturers advise against using it in critical joints (NASA fastener guidelines say no).

They make a difference on small screws at modest torques, where the trailing edge bites down in the screw seat, and they do the same on other equipment that needs them. Don’t use a flat washer with one, don’t reuse one after flattening it, and don’t use one on soft plastic or aluminum seat materials which they'll chew up.

These measurements is in inches only. Use the DIN 127B table above if you have metric machinery; do not convert from this table for those units. The series are not interchangeable, and the closest metric washer often has a section difference of more then the allowed range.

From the table you can see what bolt size you have, and then you read across that row. The nominal inside diameter (ID) is d1 (mm). For the smaller sizes this corresponds with a normal ISO 7089 washer through M16.

The nominal outside diameter (OD) is d2 (mm). The nominal thickness (s) is in mm. The working rule for the larger series is OD vs bolt dia. The outside diameter are approximately 3 times the bolt size.

These are the metric equivalent to penny or fender washers. They are big thin discs which spread the load from a small bolt across as large an area as possible. They are used on through-bolts in plaster board, soft timber, fibreglass and thin sheet material. Also used where there is an enlarged or ragged hole; where the hole is slotted.

There is a stiffness trade-off. Wide thin disc will cup up beneath a heavily torqued bolt. It is therefore used on low-to-moderate preload joints. It is not used underneath a fully torqued grade 8.8 bolt bearing on steel.

I notice that’s where it breaks convention and DIN 9021 uses a looser hole than the normal series from M18 on up. For M18, they have a hole 20 mm across; for M20, a hole 22 mm across; for M24, a hole 26 mm across. And this is what leads to them being nearly exclusively used above slotted or oversized holes.

To figure out what size of one of these big discs you’ve got, you’d measure its thickness and outside diameter. That means you don't just measure the hole.

For steel at 200 HV DIN 9021 has been merged and replaced with ISO 7093-1. For other materials or hardness it is in ISO 7093-2. In common sizes it carries over without change. So boxes stamped either way can be used interchangeably in these ranges.

Above M16 the standard thins out. There is no entry for M22, M27 and M33 so that's where the table skips. Check the drawing dimensions if a supplier offers these to you because they will be a factory standard.

The table isn't to be used with imperial fender or penny washers. That's the following table. It isn't to be used with repair washers sold as hole-in-mm x OD-in-mm. That's a UK retail convention that overlaps but isn't the same standard.

It isn't for structural uses that must carry a heavy load. In those, a thin large washer will lose its preload and dish.

The Imperial fender washer names starts with the Bolt Size followed by the Outside Diameter, so a 1/4 X 1-1/4 Washer is 1-1/4 across and holds a 1/4 in bolt. See that on the left hand side.

Next, look at the Actual ID (in), OD (in) and Thickness (in). Look at the Thickness min - max. That is the range of how thick this band might be on a standard 16-gauge fender washer.

Many of these will have multiple ODs for the same bolt size. That's where the series comes into play. You get your bolt and also know the size of the footprint.

It’s a term used in auto body work. The washer holds thin sheet metal (fenders) without pulling it through. They’re called penny washers in the UK and were once the size of an old penny.

Pick one where the fastener is stronger than the material you’re attaching it to. For example: holes that have wallowed and gotten oversized; rusty holes; plastic panels; plywood; sheet metal; drywall with toggle bolt.

The washer spreads the load out to solid material. Otherwise a normal USS or SAE washer will just pull right through the material.

The fender washer is thin for its diameter. Its nominal thickness is 0.065 in. That’s roughly 16 gauge for all of the series. When torqued with a strong bolt against it, they dishe.

Stack a thick USS washer below the fender washer for a true preload on the joint. Or take a step up to a plate.

There is heavy fender washers at 0.084 in and extra heavy at 0.132 in made by several makers. They’re there for just this purpose. But they are not a standard series; they’re catalog items.

We didn’t find a single ASME basic dimension sheet for all combinations, so each manufacturer have their own. This is what’s on hand at most big time US suppliers.

Some brands’ ID’s differ by a few thousandths. The 3/16 in bore is the worst offender. From 0.209 to 0.233 in it goes.

None of this stuff is hardened. For load rated and structural applications, you should of get an engineered plate washer or use an F436 washer.

The table above is the DIN 9021 list of metric equivalents. When crossing systems, match on hole and measured OD, not name.

The 1/4 x 1-1/4 fender washer is 6.4 x 31.8 mm. That fits between the DIN 9021 M6 disc (18 mm) and the M10 disc (30 mm) from the same system.

When bridging systems, metric fender washers is selected by footprint different than by bolt size.

So what do these numbers mean? First, this table act as the decision layer. It names the family in the Washer series and the document containing the family in the Standard column. It then reveals the OD relative to bolt, which shows how big the footprint will be compared to the bolt diameter. Next are the Typical thickness ranges across the size run. Finally, the rule of thumb in the Choose it when column provide a one-liner to get you started. After that, find your series and leap to the corresponding table above for the precise dimension.

If you have a good hole and are using steel on steel, you want just the regular series (e.g., SAE or ISO 7089). Oversized holes, timber, sheet metal bump you up to USS, and fender washers bumps you up again.

Tight counterbores or narrow flanges pushes you to move from USS to SAE, or from ISO 7089 to the smaller OD ISO 7092 series.

The most frequent ordering error is mixing systems. A 6.4 mm hole M6 washer slips onto a 6.35 mm dia. It is a 1/4 in bolt. An SAE 1/4 washer with a 7.1 mm hole (.281 in) fits an M6 bolt loosely. They both go together, but now the thickness and OD don't match what's called out on the drawing.

Order the washer in the same system as the bolt. If you're not sure of your stock measure, measure all 3 sizes and match them against a table.

Speaking of washers, there is one more that calls for a caution: Split lock washers live by legend drawing and inertia more than efficacy. Moddern locking references point elsewhere. DIN revoked DIN 127 and that points the same way if you really want to tighten a joint that has come loose under use.

Use threadlocker, serrated flange fasteners, wedgelocking pairs of washer, or prevailing torque nuts. Reserve split washers for low preload screws where they can still bite.

But don’t ignore hardness. All but the 300 HV class (ISO 7089) of what I’ve listed here are general purpose, soft parts. Soft washers embed and bleed off preload under high strength bolt like A325/A490 or grade 10.9/12.9.

For such joints, specify hardened washers at the get-go. For this you should of want ISO 7089 300 HV, ASTM F436, or EN 14399.