Wrist pin

1. A piston assembly, comprising:

a piston having a wrist pin bore;

a connecting rod having a wrist pin bore; and

a wrist pin receivable in said bores to connect said piston to said connecting rod, said wrist pin having an outer surface roughness no greater than 0.10 μm, a Kurtosis value that is inversely proportional to said surface roughness such that the product of said Kurtosis value and said surface roughness is between about 0.3 μm to 0.6 μm, a skewness of about −1.0 to 0.0, and a lay angle relative to an axis of said wrist pin of 85 to 95 degrees.

2. The piston assembly of claim 1 , wherein said wrist pin bores are bushingless and covered by a low friction coating.

3. The piston assembly of claim 2 , wherein said low friction coating comprises manganese phosphate.

4. The piston assembly of claim 1 , wherein said piston includes a piston body formed with said wrist pin bore and a piston skirt formed as one piece with said piston body of the same material.

5. A wrist pin for joining a connecting rod to a piston, said wrist pin comprising:

a generally cylindrical wrist pin body having a central longitudinal axis and a outer surface; and

wherein said outer surface is characterized by having an outer surface roughness of no greater than 0.10 μm, a Kurtosis value that is inversely proportional to the surface roughness such that the product of the Kurtosis valve and the surface roughness is between 0.3 μm and 0.60 μm, a skewness of about −1.0 to 0.0 and a lay angle relative to the axis of rotation of about 85 to 95 degrees.