Flat Washer

Standard: ANSI/ASME B18.22.1, DIN125
Size: 3/8″ – 4″, M6-M100
Material: Hastelloy, Monel, Nickel, Inconel, Incoloy, Duplex, Superalloy, Austenitic Stainless steel 
Heat Treatment: Solution and Aging

What is a flat washer?

Flat washers are usually thin parts of various shapes, which are used to reduce friction, prevent leakage, isolate, prevent loosening or disperse pressure. Many materials and structures have such components to perform various similar functions. Limited by the material and process of threaded fasteners, the bearing surface of fasteners such as bolts is small. Therefore, in order to reduce the compressive stress on the bearing surface and protect the surface of the connected parts, washers are used. In order to prevent the loosening of the connecting pair, anti loose spring washer, multi tooth lock washer, round nut stop washer and saddle shaped, corrugated and conical elastic washer are used.
The flat washer is mainly used to reduce the pressure. When the tightening axial force of some parts is very large, it is easy to press the washer into a dish shape. At this time, it can be solved by using materials and improving the hardness.

International standard for flat washers

Flat Washer Per. ISO 7089 Size Table
All size units given in mm

For Screw Nominal Size	Hole Diameter	Outside Diameter	Washer Thickness
M1.6	1.7	4	0.3
M2	2.2	5	0.3
M2.5	2.7	6	0.5
M2.6	2.8	7	0.5
M3	3.2	7	0.5
M3.5	3.7	8	0.5
M4	4.3	9	0.8
M5	5.3	10	1
M6	6.4	12	1.6
M7	7.4	14	1.6
M8	8.4	16	1.6
M10	10.5	20	2
M12	13	24	2.5
M14	15	28	2.5
M16	17	30	3
M18	19	34	3
M20	21	37	3
M22	23	39	3
M24	25	44	4
M27	28	50	4
M30	31	56	4
M33	34	60	5
M36	37	66	5
M39	40	72	6
M42	43	78	7
M45	46	85	7
M48	50	92	8
M52	54	98	8
M56	58	105	9

Flat Washer Per. ISO 7416 Size Chart
All size units given in mm

Nominal Size	Hole Dia	Outside Dia	Washer Thick
12.0000	13.0000	25.0000	4.60000
16.0000	17.0000	33.0000	4.60000
20.0000	21.0000	40.0000	4.60000
24.0000	25.0000	47.0000	4.60000
30.0000	31.0000	56.0000	5.60000
36.0000	37.0000	66.0000	5.60000

BS 4320 Plain Washer, Black Metric Series

All dimensions in mm.

Designation (thread diameter)a	Internal diameter d1		External diameter d2		Thickness s
	max.	min.	max.	min.	Thick (normal)
					max.	min.
M5	5.8	5.5	10.0	9.2	1.2	0.8
M6	7.0	6.6	12.5	11.7	1.9	1.3
(M7)	8.0	7.6	14.0	13.2	1.9	1.3
M8	9.4	9.0	17.0	16.2	1.9	1.3
M10	11.5	11.0	21.0	20.2	2.3	1.7
M12	14.5	14.0	24.0	23.2	2.8	2.2
(M14)	16.5	16.0	28.0	27.2	2.8	2.2
M16	18.5	18.0	30.0	29.2	3.6	2.4
(M18)	20.6	20.0	34.0	32.8	3.6	2.4
M20	22.6	22.0	37.0	35.8	3.6	2.4
(M22)	24.6	24.0	39.0	37.8	3.6	2.4
M24	26.6	26.0	44.0	42.8	4.6	3.4
(M27)	30.6	30.0	50.0	48.8	4.6	3.4
M30	33.8	33.0	56.0	54.5	4.6	3.4
(M33)	36.8	36.0	60.0	58.5	6.0	4.0
M36	39.8	39.0	66.0	64.5	6.0	4.0
(M39)	42.8	42.0	72.0	70.5	7.0	5.0
M42	45.8	45.0	78.0	76.5	8.2	5.8
(M45)	48.8	48.0	85.0	83.0	8.2	5.8
M48	53.0	52.0	92.0	90.0	9.2	6.8
(M52)	57.0	56.0	98.0	96.0	9.2	6.8
M56	63.0	62.0	105.0	103.0	10.2	7.8
(M60)	67.0	66.0	110.0	108.0	10.2	7.8
M64	71.0	70.0	115.0	113.0	10.2	7.8
(M68)	75.0	74.0	120.0	118.0	11.2	8.8

BS 4320 Plain Washer, Black Metric Series

All dimensions in mm.

Designation (thread diameter)a	Internal diameter d1		External diameter d2		Thickness s
	max.	min.	max.	min.	Thick (normal)
					max.	min.
M5	5.8	5.5	10.0	9.2	1.2	0.8
M6	7.0	6.6	12.5	11.7	1.9	1.3
(M7)	8.0	7.6	14.0	13.2	1.9	1.3
M8	9.4	9.0	17.0	16.2	1.9	1.3
M10	11.5	11.0	21.0	20.2	2.3	1.7
M12	14.5	14.0	24.0	23.2	2.8	2.2
(M14)	16.5	16.0	28.0	27.2	2.8	2.2
M16	18.5	18.0	30.0	29.2	3.6	2.4
(M18)	20.6	20.0	34.0	32.8	3.6	2.4
M20	22.6	22.0	37.0	35.8	3.6	2.4
(M22)	24.6	24.0	39.0	37.8	3.6	2.4
M24	26.6	26.0	44.0	42.8	4.6	3.4
(M27)	30.6	30.0	50.0	48.8	4.6	3.4
M30	33.8	33.0	56.0	54.5	4.6	3.4
(M33)	36.8	36.0	60.0	58.5	6.0	4.0
M36	39.8	39.0	66.0	64.5	6.0	4.0
(M39)	42.8	42.0	72.0	70.5	7.0	5.0
M42	45.8	45.0	78.0	76.5	8.2	5.8
(M45)	48.8	48.0	85.0	83.0	8.2	5.8
M48	53.0	52.0	92.0	90.0	9.2	6.8
(M52)	57.0	56.0	98.0	96.0	9.2	6.8
M56	63.0	62.0	105.0	103.0	10.2	7.8
(M60)	67.0	66.0	110.0	108.0	10.2	7.8
M64	71.0	70.0	115.0	113.0	10.2	7.8
(M68)	75.0	74.0	120.0	118.0	11.2	8.8

ISO BS EN DIN 4320 Plain Washer, Bright Metric Series

All dimensions in mm.

Designation (thread diameter)a	Internal diameter d1		External diameter d2		Thickness s
	max.	min.	max.	min.	Thick (normal)		Thin
					max.	min.	max.	min.
M1.0	1.25	1.1	2.5	2.3	0.4	0.2	–	–
M1.2	1.45	1.3	3.0	2.8	0.4	0.2	–	–
(M1.4)	1.65	1.5	3.0	2.8	0.4	0.2	–	–
M1.6	1.85	1.7	4.0	3.7	0.4	0.2	–	–
M2.0	2.35	2.2	5.0	4.7	0.4	0.2	–	–
(M2.2)	2.55	2.4	5.0	4.7	0.6	0.4	–	–
M2.5	2.85	2.7	6.5	6.2	0.6	0.4	–	–
M3	3.4	3.2	7.0	6.7	0.6	0.4	–	–
(M3.5)	3.9	3.7	7.0	6.7	0.6	0.4	–	–
M4	4.5	4.3	9.0	8.7	0.9	0.7	–	–
(M4.5)	5.0	4.8	9.0	8.7	0.9	0.7	–	–
M5	5.5	5.3	10.0	9.7	1.1	0.9	–	–
M6	6.7	6.4	12.5	12.1	1.8	1.4	0.9	0.7
(M7)	7.7	7.4	14.0	13.6	1.8	1.4	0.9	0.7
M8	8.7	8.4	17.0	16.6	1.8	1.4	1.1	0.9
M10	10.9	10.5	21.0	20.5	2.2	1.8	1.45	1.05
M12	13.4	13.0	24.0	23.5	2.7	2.3	1.8	1.4
(M14)	15.4	15.0	28.0	27.5	2.7	2.3	1.8	1.4
M16	17.4	17.0	30.0	29.5	3.3	2.7	2.2	1.8
(M18)	19.5	19.0	34.0	33.2	3.3	2.7	2.2	1.8
M20	21.5	21.0	37.0	36.2	3.3	2.7	2.2	1.8
(M22)	23.5	23.0	39.0	38.2	3.3	2.7	2.2	1.8
M24	25.5	25.0	44.0	43.2	4.3	3.7	2.7	2.3
(M27)	28.5	28.0	50.0	49.2	4.3	3.7	2.7	2.3
M30	31.6	31.0	56.0	55.0	4.3	3.7	2.7	2.3
(M33)	34.6	34.0	60.0	59.0	5.6	4.4	3.3	2.7
M36	37.6	37.0	66.0	65.0	5.6	4.4	3.3	2.7
(M39)	40.6	40.0	72.0	71.0	6.6	5.4	3.3	2.7

American Metric Washers ANSI B18.22M Size Table

American National Standard Metric Plain Washers

Washer Sizea	Washer Series	Inside Diameter A		Outside Diameter B		Thickness C
		Max	Min	Max	Min	Max	Min
1.6	Narrow Regular Wide	2.09 2.09 2.09	1.95 1.95 1.95	4.00 5.00 6.00	3.70 4.70 5.70	0.70 0.70 0.90	0.50 0.50 0.60
2	Narrow Regular Wide	2.64 2.64 2.64	2.50 2.50 2.50	5.00 6.00 8.00	4.70 5.70 7.64	0.90 0.90 0.90	0.60 0.60 0.60
2.5	Narrow Regular Wide	3.14 3.14 3.14	3.00 3.00 3.00	6.00 8.00 10.00	5.70 7.64 9.64	0.90 0.90 1.20	0.60 0.60 0.80
3	Narrow Regular Wide	3.68 3.68 3.68	3.50 3.50 3.50	7.00 10.00 12.00	6.64 9.64 11.57	0.90 1.20 1.40	0.60 0.80 1.00
3.5	Narrow Regular Wide	4.18 4.18 4.18	4.00 4.00 4.00	9.00 10.00 15.00	8.64 9.64 14.57	1.20 1.40 1.75	0.80 1.00 1.20
4	Narrow Regular Wide	4.88 4.88 4.88	4.70 4.70 4.70	10.00 12.00 16.00	9.64 11.57 15.57	1.20 1.40 2.30	0.80 1.00 1.60
5	Narrow Regular Wide	5.78 5.78 5.78	5.50 5.50 5.50	11.00 15.00 20.00	10.57 14.57 19.48	1.40 1.75 2.30	1.00 1.20 1.60
6	Narrow Regular Wide	6.87 6.87 6.87	6.65 6.65 6.65	13.00 18.80 25.40	12.57 18.37 24.88	1.75 1.75 2.30	1.20 1.20 1.60
8	Narrow Regular Wide	9.12 9.12 9.12	8.90 8.90 8.90	18.80 b 25.40 b 32.00	18.37 b 24.48 b 31.38	2.30 2.30 2.80	1.60 1.60 2.00
10	Narrow Regular Wide	11.12 11.12 11.12	10.85 10.85 10.85	20.00 28.00 39.00	19.48 27.48 38.38	2.30 2.80 3.50	1.60 2.00 2.50
12	Narrow Regular Wide	13.57 13.57 13.57	13.30 13.30 13.30	25.40 34.00 44.00	24.88 33.38 43.38	2.80 3.50 3.50	2.00 2.50 2.50
14	Narrow Regular Wide	15.52 15.52 15.52	15.25 15.25 15.25	28.00 39.00 50.00	27.48 38.38 49.38	2.80 3.50 4.00	2.00 2.50 3.00
16	Narrow Regular Wide	17.52 17.52 17.52	17.25 17.25 17.25	32.00 44.00 56.00	31.38 43.38 54.80	3.50 4.00 4.60	2.50 3.00 3.50
20	Narrow Regular Wide	22.32 22.32 22.32	21.80 21.80 21.80	39.00 50.00 66.00	38.38 49.38 64.80	4.00 4.60 5.10	3.00 3.50 4.00
24	Narrow Regular Wide	26.12 26.12 26.12	25.60 25.60 25.60	44.00 56.00 72.00	43.38 54.80 70.80	4.60 5.10 5.60	3.50 4.00 4.50
30	Narrow Regular Wide	33.02 33.02 33.02	32.40 32.40 32.40	56.00 72.00 90.00	54.80 70.80 88.60	5.10 5.60 6.40	4.00 4.50 5.00
36	Narrow Regular Wide	38.92 38.92 38.92	38.30 38.30 38.30	66.00 90.00 110.00	64.80 88.60 108.60	5.60 6.40 8.50	4.50 5.00 7.00

• 
  a Nominal washer sizes are intended for use with comparable screw and bolt sizes.

• b The 18.80 ⁄18.37 and 25.40 ⁄24.48 mm outside diameters avoid washers which could be used in coin-operated devices.

• All dimensions are in millimeters.