opening wedge

Then you think the lack of rifling on the bullet might be the opening wedge to catching the man who shot Stockbridge?

A glare of light struck his eyes as the opening wedge widened.

Benda, the Italian fruit-dealer on the corner, Meyer had marked finally as his opening wedge in the little clannish community.

To the public it is highly dangerous as a precedent; it will operate as an opening wedge to other claims without limitation.

It was the opening wedge which shivered the transatlantic branches from the parent stock.