Hmmh ...., hard to tell. Here is our little slip clutch story: We ran two eight row heads and two twelve row heads, all new, last year. Right the first day, I broke a set of slip clutch bolts. Through that, I found out that the two twelve row heads had different slip clutches. One of them, which I will call the "old style", had the beefy 16mm bolts in and was built stronger. Its serial number tag also said "Made in Italy". The other twelve row and both eight row heads had the smaller 14mm bolts and a weaker design slip clutch in. Their serial number tag said "Assembled in America" on. That lead to the conclusion, that the later model corn heads had a weaker slip clutch. We went through lots of bolts, but never broke the clutch itself.