12.9 Hex bolt(Coarse Steel Unplated 20X220 Pitch 2.5

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This is a bolt with a strength class of 12.9, stamped with "12.9" on the head.
It has a regular hexagonal head and is tightened using a wrench or spanner.
It can be tightened more securely than slotted or cross recessed screws.
●Full thread = A bolt where the entire length below the head is threaded. (General guideline: lengths of 30mm or less)
●Partial thread (medium bolt) = A bolt that is only threaded from the tip partway up the shank.
Partial thread length calculation method (approximate guideline)
L = up to 129     Nominal thread diameter × 2 + 6
L = 130 to 219   Nominal thread diameter × 2 + 12
L = 220 and above   Nominal thread diameter × 2 + 25
Example: For an M10×250 partial thread bolt, since L (length) is 220 or more: 10×2+25 = 45mm of threaded length.
Thread Pitch & Hex Width Across Flats Reference　Hex Bolt Encyclopedia

• 12.9 Hex bolt Coarse pitch
• Nominal thread diameter M20
• Length under head (ℓ) 220.0 Partial thread Thread length 52
• Coarse pitch 2.5
• Width across flats (s) Nominal 30 Tolerance 0,-0.35
• Head height (k) Nominal 13 Tolerance ±0.2
• Body thickness (ds) Basic dimension 20 Tolerance 0,-0.2