Metric Fastener Hardness Class Chart

Property Class

Mechanical Property

8.8

4.8

5.6

5.8

6.8

To M16

Over M16

9.8

10.9

12.9

Tensile Strength       nom

400

500

600

800

800

900

1000

1200

Rm, N/mm               min

420

500

520

600

800

830

900

1040

1220

Brinell                      min

124

147

152

181

219

242

266

295

353

Hardness                 max

238

285

319

342

363

412

HRB

71

79

82

89

-

-

-

-

-

Rockwell                  HRC

-

-

-

-

20

23

28

32

39

Hardness                 HRB

95

99

-

-

-

-

-

HRC

-

-

-

-

32

34

37

39

44

Vickers                     min

130

155

160

190

250

255

290

320

385

Hardness                  max

250

320

336

360

380

435

Yield Stress              nom

320

300

400

480

-

-

-

-

-

ReL, N/mm                min

340

300

420

480

-

-

-

-

-

Stress at permanent  nom

-

640

640

720

900

1080

Set Limit N/mm         min

-

640

660

720

940

1100