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I'm not sure what the insert is. The entire lower ball joint itself is an insert. The unit is pressed in and out. There is a snap ring to guarantee that it doesn't come out. On some vehicles, the snap ring is not used. If the mechanic gives you a parts list, you can just take the part number of the insert and plug that number into google and see what comes up.

There is also an insertion tool that is used to press the lower ball joint out and back in. Perhaps they are just missing the tool or the adapter to fit the Nissan.

Thanks for the info. My grown son is over 100 miles away near Seattle. He has taken it to a mechanic at a well known tire chain (Les Schwab). He's used them before, and he tells me they do good work. Apparently, it took them all day to do the top ball joints and he is to return this weekend to have the bottom completed. He had mentioned that they said they might have to 'torch' them off as they are frozen due to road salt used during winter months. We will text our son and ask about the insertion tool to press it out and back in. I'll let you know what happens; he's usually very busy during the week. It will be sometime this weekend or early next week before I know the outcome. Thanks again.