could be a catch/latch wheel ?

[rotater]

fletcher
have realized the tongs action is reversed, would need long levers and weights to create a grab action using scissors.
the pic below shows the basic principle
this would be easier to make using gears, have excluded the weighted levers.

[wheelrite]

Here's a latch/catch/sear sketch I did several years ago ...
Regards
Jon

[rotater]

i placed this in community buzz

[path_finder]

dear rotater,
I recommend to you the second mechanism (from 0:26 to 0:49) of this Autodesk animation:
http://www.youtube.com/watch?v=MXPyqmNsUME