You read it right, 4340 vs. 4340. Not all 4340 Chromoly Axle Shafts are created equal. I’m going to attempt to explain this without bashing anyones product as much as possible, but the number one question I hear about axle shafts is, “why would I buy Superior Axle 4340 chromoly axle shafts when brand X has 4340 chromoly axle shafts for cheaper, and have a no questions asked warranty?” One the of the biggest and simplest answer is, brand X’s 4340 chromoly…. isn’t the same as US 4340.