Machine Design
A flanged pipe joint will be a leak-proof joint, if the circumferential pitch of the bolts is (where d = Diameter of bolt hole)

Greater than 30d
Between 20d and 30d
Equal to inside diameter of pipe
Less than 20d

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

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

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