Machine Design
According to Indian standards, a bolt thread of 6 mm size of coarse pitch and with allowance on the threads and normal tolerance grade is designated as

M8 - 6d
M6
M8
M6 - 8d

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Machine Design
In oilness bearings

The oil film pressure is generated only by the rotation of the journal
Do not require external supply of lubricant
The oil film is maintained by supplying oil under pressure
Grease required to be applied after some intervals

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