Machine Design
An alien bolt is

Self locking bolt
Provided with hexagonal depression in head
Used in high speed components
Same as stud

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Machine Design
The ends of the leaves of a semi-elliptical leaf spring are made triangular in order to

Obtain variable moment of inertia (I) in each leaf
Make M/I constant throughout the length of the leaf
Have variable bending moment (M) in each leaf
Permit each leaf to act as an overhanging beam

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