The Erson aluminum roller rocker arms are complete JUNK. They are cast and of extremely low quality. I bought a set of these once because they were considerably cheaper than anything else on the market and I soon found out why. I was degreeing the cam and decided to check gross valve lift as compared to lobe lift to verify the rocker arm ratio and not one in the box was the 1.6 ratio they had been advertised as (they were all closer to 1.5) and the variance between each individual arm was all over the map. I returned the set thinking I got a bad set and got another....two sets later I was tired of checking and determined that the product was complete JUNK so I returned them and spent the extra cash to get the Ford Motorsports set. I now have 3 sets of the Ford Motorsports ones and they are of the highest quality and always check right on the money, I guess that is why I own 3 sets.