Hi All - RA and RS are two of the top scoring 20 specs for a bowling ball.  RA and RS are measurements for the height and width of the surface roughness of a ball.  Surface roughness is key to ball performance.  At the microscopic level you can see these peaks and valleys.  But you never see anything written about either except in a brief phrase in a BJ Ball review or in a USBC research paper.  Just wondering! Thank you and stay safe. 

The USBC does establish that the surface roughness (Ra) of any individual ball 13.0 lbs or greater cannot exceed 65 micro inches, and the average for all balls within a weight class cannot exceed 50 micro inches.  If a ball manufacturer submits a test ball for approval, and the ball has an Ra of 42 micro inches or greater, the USBC then requires 8 additional test balls to make sure that the Ra of any single ball is not greater than 65, and that the average of all balls does not exceed 50.

Ra is important, but it is just one aspect of the coverstock of a ball.  Oil absorption rate of the cover is just as important as the surface texture.  A "rough" ball with an absorbent cover is going to be an absolute snow tire on a bowling lane.