Sheared seat post bolt - why?

[CharleyFarley]

Surprised not to see ridges on the curved surface - and the curve seems 90 degrees 'wrong'.

Why would it have ridges? That curve goes from side to side, not front to back. It looks strange to me.

 

[Biker BoB]

The ridges give it bite so it doesn't slip.
This means only the thicknes of each ridge is the adjustment difference rather than a smooth adjustment curve.
They need this ridge to remain in place without over tightening the clamp

 

[Ajax Bay]

Why would it have ridges? That curve goes from side to side, not front to back. It looks strange to me.

You're right: the image the OP has harvested off the net looks strange.
How can the pitch of the seat be adjusted?

 

[Biker BoB]

You're right: the image the OP has harvested off the net looks strange.
How can the pitch of the seat be adjusted?

In the picture of the red clamp it's adjustable on the seat pin and bottom part of the clamp..

 

[Ajax Bay]

OP has not been back for days, so clearly not really interested.
I'd expect the "bottom part of the clamp" to be both curved and ridged: in the image it looks straight.
Let's see an image of the actual broken clamp, though YS has offered an answer, independent of the actual (single bolt)seat clamp's design.