Inputs
Nominal size (M5 to M24), equal to the nominal thread diameter of the matching bolt or nut.
Bolts · dimensions
ISO 7089 Plain Washer Dimensions
ISO 7089 standardizes normal-series plain washers for bolts and nuts of the same nominal thread diameter. The hole diameter sets the clearance to the fastener, and the outer diameter sets the bearing area under head or nut -- and with it the bearing pressure, relevant for soft materials or slotted holes.
Matching bolt: ISO 4014 dimensions. Bearing pressure under the head: Tightening Torque.
ISO7089
02
Standard dimensions
Enter nominal size.
Inputs and method
Size a plain washer to ISO 7089
Determine hole diameter, outer diameter and thickness of a normal-series plain washer from nominal size.
Calculation
A pure table lookup from Table 1 (preferred sizes) of the standard: hole diameter, outer diameter and thickness are fixed per nominal size.
Example
M10: hole diameter d1 between 10.50 mm and 10.77 mm, outer diameter d2 between 19.48 mm and 20.00 mm, nominal thickness h 2 mm.
Sources and limits: DIN EN ISO 7089:2000-11, Table 1.
Size a plain washer to ISO 7089 in detail
Determine hole diameter, outer diameter and thickness of a normal-series plain washer from nominal size.
Why does the washer's outer diameter matter?
A bolted joint transmits its preload into the clamped part through the head or nut bearing area. Without a washer, that area is limited by the head or nut diameter; a washer to ISO 7089 enlarges it to the washer's outer diameter d2. With soft materials, coated surfaces or slotted holes, the larger area prevents the head from sinking in or overloading the part locally -- bearing pressure falls proportionally with area, i.e. with d2 squared.
Formula and variables
A pure table lookup from Table 1 (preferred sizes) of the standard: hole diameter, outer diameter and thickness are fixed per nominal size.
Choose the inputs correctly
Nominal size (M5 to M24), equal to the nominal thread diameter of the matching bolt or nut.
How to use the calculator
Select the nominal size of the bolt or nut the washer must fit. The calculator returns hole diameter, outer diameter and thickness directly from Table 1.
Worked example
M10: hole diameter d1 between 10.50 mm and 10.77 mm, outer diameter d2 between 19.48 mm and 20.00 mm, nominal thickness h 2 mm.
Which dimensions actually drive the design?
The hole diameter d1 (min = nominal) sets the radial clearance to the bolt and must match the chosen clearance hole (ISO 273). The outer diameter d2 (min) is the value to use for a bearing-pressure calculation -- not the nominal size, which only states the maximum. Thickness h feeds into the clamp-length calculation to VDI 2230 and must be accounted for when choosing bolt length.
All dimensions in millimetres.
Typical applications
Selecting the matching washer size for a bolt, bearing-pressure calculation under head or nut, clamp-length calculation to VDI 2230.
Assumptions, limits and common mistakes
DIN EN ISO 7089:2000-11, Table 1.
Common mistake: Don't use the nominal outer diameter (= maximum) for a bearing-pressure calculation -- the minimum outer diameter d2,min governs a conservative estimate of the bearing area.
Frequently asked questions
Which washer size fits an M10 bolt?
A washer ISO 7089 - 10, with hole diameter 10.50 to 10.77 mm, outer diameter 19.48 to 20.00 mm and nominal thickness 2 mm.
What's the difference between Table 1 and Table 2 of the standard?
Table 1 lists the preferred sizes covered by this calculator. Table 2 lists additional intermediate sizes (e.g. M14, M18) that should be avoided in practice, for special cases only.