10/12/2025
๐ฉ ๐๐จ๐ฅ๐ญ ๐๐ซ๐๐๐๐ฌ ๐.๐, ๐.๐, ๐๐.๐ & ๐๐.๐ โ ๐๐ก๐๐ญ ๐๐จ ๐๐ก๐๐ฌ๐ ๐๐ฎ๐ฆ๐๐๐ซ๐ฌ ๐๐๐๐ง?
โ
Those numbers stamped on metric bolts arenโt random, they tell you the strength class of the bolt.
โ
Hereโs the simple breakdown ๐
โ๏ธ ๐๐จ๐ฐ ๐๐จ๐ฅ๐ญ ๐๐ซ๐๐๐๐ฌ ๐๐จ๐ซ๐ค?
A grade like 8.8 or 10.9 has two parts:
๐๐ก๐ ๐๐ข๐ซ๐ฌ๐ญ ๐ง๐ฎ๐ฆ๐๐๐ซ ร ๐๐๐ = ๐ฆ๐ข๐ง๐ข๐ฆ๐ฎ๐ฆ ๐ญ๐๐ง๐ฌ๐ข๐ฅ๐ ๐ฌ๐ญ๐ซ๐๐ง๐ ๐ญ๐ก (๐๐๐)
โ Example: 8.8 = 800 MPa, 10.9 = 1000 MPa, 12.9 = 1200 MPa
โ
๐๐ก๐ ๐ฌ๐๐๐จ๐ง๐ ๐ง๐ฎ๐ฆ๐๐๐ซ (๐๐ฌ ๐ ๐๐๐๐ข๐ฆ๐๐ฅ) = ๐ฒ๐ข๐๐ฅ๐ ๐ฌ๐ญ๐ซ๐๐ง๐ ๐ญ๐ก ๐ซ๐๐ญ๐ข๐จ
โ Example: 12.9 = 90% yield, meaning it permanently deforms at 90% of its tensile strength.
โ
This makes bolt grades a quick way to understand how much load the bolt can safely handle.
โ
โ๏ธ ๐๐ซ๐๐๐ ๐.๐ โ ๐๐ข๐ฅ๐ ๐๐ญ๐๐๐ฅ (๐๐ข๐ ๐ก๐ญ ๐๐ฎ๐ญ๐ฒ)
โข Tensile โ 400 MPa
โข Used for light structures, furniture, non-critical joints
โข Basic, economical bolt
โ
โ๏ธ ๐๐ซ๐๐๐ ๐.๐ โ ๐๐ข๐ ๐ก-๐๐๐ง๐ฌ๐ข๐ฅ๐ (๐๐จ๐ฌ๐ญ ๐๐จ๐ฆ๐ฆ๐จ๐ง)
โข Tensile โ 800 MPa
โข โStandard strong boltโ in construction & machinery
โข Great balance of strength + cost
โ
โ๏ธ ๐๐ซ๐๐๐ ๐๐.๐ โ ๐๐๐ซ๐ฒ ๐๐ข๐ ๐ก ๐๐ญ๐ซ๐๐ง๐ ๐ญ๐ก (๐๐ฅ๐ฅ๐จ๐ฒ ๐๐ญ๐๐๐ฅ)
โข Tensile โ 1000 MPa
โข Used for automotive, heavy machinery, high clamp loads, vibration areas
โข Stronger & harder than 8.8
โ
โ๏ธ ๐๐ซ๐๐๐ ๐๐.๐ โ ๐๐ฅ๐ญ๐ซ๐ ๐๐ข๐ ๐ก ๐๐ญ๐ซ๐๐ง๐ ๐ญ๐ก (๐๐ฅ๐ฅ๐จ๐ฒ ๐๐ญ๐๐๐ฅ)
โข Tensile โ 1200 MPa
โข For critical, high-stress connections where failure is not an option
โข Not used for normal structural steel unless specified by engineers
โ
โ๏ธ Simple Rule of Thumb
๐๐ข๐ ๐ก๐๐ซ ๐ง๐ฎ๐ฆ๐๐๐ซ = ๐ก๐ข๐ ๐ก๐๐ซ ๐ฌ๐ญ๐ซ๐๐ง๐ ๐ญ๐ก,
but always choose based on engineering requirements โ higher isnโt always better.
โ
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โ