What is in it

Please check attachment i want to make this type of clamp to hold casting part on cnc milling machine..can some one define it what is the working principle that clamp...

Regards
Asif

The part is sitting on locating pins in the clamp body, the screws contact pins on the other end of the clamp thus, when tightened, clamp the part down to the locating pins by a rocking action.

Right. Not quite toggle clamps and not quite toe clamps, but rocker toe clamps sounds about right.

I have always thought they were hydraulic rather than mechanical, either way I am not clear how they actually clamp the workpiece to the bed because in principal the work piece can still "float vertically", surely there must be other clamps to hold the piece down or am I not seeing it right.

They look hydraulic to me as well. Looks like the stainless pins are floating, connected by hydraulic fluid, so when you push down on one pin the other pushes up.
Not sure how the piece is held down. Maybe the clamps are biased strongly down by internal springs or something?

I found whats in this devices...this device work on wedge system..3 pins ... which is link with each other thru inclined plane...

Check jpeg

I can understand your drawing and how it clamps the work piece, but it is not clear to me how it clamps the work piece to the bed because it is essentially floating in principle. I guess they would help stop vibration and chattering but the work piece can still rock unless there is additional clamping. Dave