DIN 125 flat washers

Flat washers according to DIN 125 (forms A and B) are standardized fasteners that distribute the load of bolts and nuts. Version A lacks a chamfer, while version B has a slight chamfer on the inner and outer edges. Below are the standard dimensions, international equivalents and technical data relevant for selection.

Standard dimensions

Nominal bolt size	d1 (min.)	d2 (max.)	s (thickness)
M1.6	1,7 mm / 0.067 in	4,0 mm / 0.157 in	0,3 mm / 0.012 in
M2	2,2 mm / 0.087 in	5,0 mm / 0.197 in	0,3 mm / 0.012 in
M2.5	2,7 mm / 0.106 in	6,0 mm / 0.236 in	0,5 mm / 0.020 in
M3	3,2 mm / 0.126 in	7,0 mm / 0.276 in	0,5 mm / 0.020 in
M3.5	3,7 mm / 0.146 in	8,0 mm / 0.315 in	0,5 mm / 0.020 in
M4	4,3 mm / 0.169 in	9,0 mm / 0.354 in	0,8 mm / 0.031 in
M5	5,3 mm / 0.209 in	10,0 mm / 0.394 in	1,0 mm / 0.039 in
M6	6,4 mm / 0.252 in	12,0 mm / 0.472 in	1,6 mm / 0.063 in
M8	8,4 mm / 0.331 in	16,0 mm / 0.630 in	1,6 mm / 0.063 in
M10	10,5 mm / 0.413 in	20,0 mm / 0.787 in	2,0 mm / 0.079 in
M12	13,0 mm / 0.512 in	24,0 mm / 0.945 in	2,5 mm / 0.098 in
M14	15,0 mm / 0.591 in	28,0 mm / 1.102 in	2,5 mm / 0.098 in
M16	17,0 mm / 0.669 in	30,0 mm / 1.181 in	3,0 mm / 0.118 in
M18	19,0 mm / 0.748 in	34,0 mm / 1.339 in	3,0 mm / 0.118 in
M20	21,0 mm / 0.827 in	37,0 mm / 1.457 in	3,0 mm / 0.118 in
M22	23,0 mm / 0.906 in	39,0 mm / 1.535 in	3,0 mm / 0.118 in
M24	25,0 mm / 0.984 in	44,0 mm / 1.732 in	4,0 mm / 0.157 in
M27	28,0 mm / 1.102 in	50,0 mm / 1.969 in	4,0 mm / 0.157 in
M30	31,0 mm / 1.220 in	56,0 mm / 2.205 in	4,0 mm / 0.157 in
M33	34,0 mm / 1.339 in	60,0 mm / 2.362 in	5,0 mm / 0.197 in
M36	37,0 mm / 1.457 in	66,0 mm / 2.598 in	5,0 mm / 0.197 in

Thickness and surface finish

DIN 125 A washers (without chamfer) have thicknesses ranging from 0.3 mm / 0.012 in for the smallest diameter to 5 mm / 0.197 in for large sizes. Version B, with chamfer, shares the same basic dimensions but requires a better edge finish. Typical surface finishes include bare steel (natural), zinc plated blue, zinc plated yellow, black-oxidized, hot dip galvanized and passivated for A2/A4 stainless steels.

Materials and hardness

Material	Typical hardness (HV)	Common designation
Carbon steel	100 – 200 HV	St, standard steel
Stainless steel A2	140 – 200 HV	AISI 304
Stainless steel A4	140 – 200 HV	AISI 316
Brass	80 – 150 HV	CuZn
Polyamide (PA)	—	Natural/black plastic

DIN 125 steel washers are often supplied in natural state or with coating. For applications under high compression, it is recommended to use washers with hardness equal to or greater than 200 HV, especially under bolts of grade 8.8 or higher.

International equivalents

DIN standard	ISO standard	Approximate ANSI/ASME standard
DIN 125 A	ISO 7089	ANSI/ASME B18.22.1 Type A (flat, similar metric)
DIN 125 B	ISO 7090	—

Although metric and imperial dimensions are not identical, in practice DIN 125 A washers can be used under UNC/UNF fasteners as long as the inner diameter is compatible. The following table shows approximate equivalents:

Metric bolt	Similar imperial bolt	Recommended DIN 125 washer
M3	#4	M3 (d1 3,2 mm / 0.126 in)
M5	#10	M5 (d1 5,3 mm / 0.209 in)
M6	1/4″	M6 (d1 6,4 mm / 0.252 in)
M8	5/16″	M8 (d1 8,4 mm / 0.331 in)
M10	3/8″	M10 (d1 10,5 mm / 0.413 in)
M12	1/2″	M12 (d1 13,0 mm / 0.512 in)
M16	5/8″	M16 (d1 17,0 mm / 0.669 in)

Torque values

DIN 125 flat washers do not alter the torque values. The tightening torque depends exclusively on the bolt, nut and friction coefficient of the system. For metric fasteners consult ISO 898-1 or DIN 13, and for unified fasteners refer to standard UNC/UNF torque tables.

Drill sizes

No specific drill is required for washers. The clearance hole must be slightly larger than the bolt outer diameter, typically between 0.2 mm / 0.008 in and 0.5 mm / 0.020 in above the nominal diameter, depending on the desired fit grade.

Allowable loads

The compressive load capacity of a flat washer is calculated as the product of the effective bearing area and the allowable stress of the material. For standard steel with yield strength ≈ 240 MPa / 34 810 psi and safety factor 1.5, the design stress is 160 MPa / 23 200 psi. The following values are approximate.

Nominal size	Bearing area	Allowable load
M6	80,9 mm² / 0,125 in²	12,9 kN / 2 900 lbf
M8	145,7 mm² / 0,226 in²	23,3 kN / 5 240 lbf
M10	227,6 mm² / 0,353 in²	36,4 kN / 8 180 lbf
M12	319,7 mm² / 0,496 in²	51,2 kN / 11 500 lbf
M16	480,0 mm² / 0,744 in²	76,8 kN / 17 260 lbf
M20	729,0 mm² / 1,130 in²	116,6 kN / 26 210 lbf

Frequently Asked Questions (FAQ)

What is the inner diameter of a DIN 125 washer for M8 bolt?

The minimum inner diameter is 8.4 mm / 0.331 in, sufficient to accommodate an M8 bolt with standard clearance.

What thickness does a DIN 125 A washer have for metric 12?

The standard thickness is 2.5 mm / 0.098 in, both for the version without chamfer and for form B.

Up to what load can an M16 carbon steel washer work?

With steel of 240 MPa / 34 810 psi yield strength and safety factor 1.5, it supports approximately 76.8 kN / 17 260 lbf in compression.

Which ISO standard corresponds to DIN 125 A?

It corresponds directly to ISO 7089, which specifies flat washers without chamfer for metric fasteners.

With what type of bolts are DIN 125 washers used?

They are commonly used with hexagonal bolts, socket head cap screws or metric Allen screws per ISO, and are also compatible with UNC/UNF fasteners if the inner diameter allows.

What constructive difference is there between DIN 125 A and DIN 125 B?

Version B incorporates a small chamfer on the inner and outer diameter (bevel of ~0.2‑0.5 mm / 0.008‑0.020 in), while version A has sharp edges.

References

• engineeringtoolbox.com: https://www.engineeringtoolbox.com/unified-screw-threads-unc-unf-d_1809.html
• bossard.com: https://www.bossard.com/global-en/eshop/products/fastening-technology/standard-fastening-elements/washers/c/01.100.300/
• mcmaster.com: https://www.mcmaster.com/products/din-125-flat-washers