This design is found in many machinist's books and is readily made in the home shop. 

The jaws were made from 12 mm square mild steel. The screws were made from stainless steel because it was on hand.

These clamps have a good feel when tightened and have good gripping force.  As shown in the photograph, a cross-hole is provided for extra tightening with a bar.  This can lead to over-tightening and slight bending of the jaws.