These are CNC made in Europe with high quality material to replace your original inserts.
 Price is for one piece. 
 
The concave surface of the ball is about 20% larger than the original, which gives a greater possibility of introducing the air flowing into the upper chamber into the swirl where the mixing occurs and is pre-ignited.
 
There are two choices of material:
-1581 Steel (30% stronger than stock, which is the same steel used for cylinder head valves)
-Inconel (Super alloy)
They fit the OM605, OM606 and OM617 engines.