My rear U-joints are starting to wear, so I figured I would replace them. I am already placing an order with RockAuto.com, well I went to add them to my order and they show several different part#s even some different sizes for the '98 blazer 4x4.

Anyone know which ones I need?

Get the U-joints locally and make sure you get Moog parts.

They have a lifetime warranty and you can claim warranty better when you get them from a local shop.