U joints too long and too thin

[Daveb]

I have a 1990 gmc k2500 4x4. I'm replacing the front driveshaft u joints. I got the replacements from autozone but when I put them in for one the caps slid right in. there was no resistance. And they wobble inside the yoke. Basically the diameter on the u joints is too small. And second they're too long. i melted the plastic out of the groove for the retainer pin but in order for one side to be behind that groove the other side sticks out 1/4 inch if not more. Am I missing something? Or did I just get the wrong size. This is my first time replacing u joints