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Bolt strength
2025-12-19
The JIS specifies 10 bolt strength grades ranging from 3.6 to 12.9. However, 99% of the bolts used in bulldozers and excavators are of grade 10.9 and 12.9, with only a very small amount being of grade 9.8 or lower.
The total number of bolts required for a 65-ton bulldozer is approximately 6,000. Among them, 12.9 grade accounts for 8.5%, 10.9 grade accounts for 8.5%, and those of 9.8 grade and below account for 1.1%.
The total number of bolts required for a 20-ton hydraulic excavator is approximately 2,000. Among them, 12.9 grade bolts account for 12.2%, 10.9 grade bolts account for 87%, and bolts of 9.8 grade and below account for 0.8%. The above proportion relationship of the bolt usage has remained unchanged for nearly 10 years.
The reason is that the working environment of construction machinery is an irregular ground and it is exposed to wind and rain. Under such heavy loads and harsh conditions, higher-strength bolts are required to achieve high axial force tightening of the components.
On the other hand, bolts with a strength exceeding 12.9 grade have higher prices and also have certain issues with anti-delay fracture resistance. Therefore, the proportion of bolt usage has remained unchanged for many years.
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