1996 GMC Suburban changing a steering knuckle

I am not exactly sure what size it is , but this is how you can calculate it, I hope this helps.

Imperial System
1 Turn on the digital caliper and set it to read in inches, not millimeters. Set the nut on a flat surface. Open the caliper jaws far enough to allow the nut to fit between them.

2 Close the caliper jaws until each jaw rests on one flat side of the nut on opposite sides.

3 Check the caliper display. The reading shows the size of the nut as a decimal. Imperial sockets are sized in fractions of an inch. See the link below for a conversion chart. Look through the table's decimal column and select the first decimal larger than your caliper reading. Select the corresponding fraction. The website Sizes has a table showing Imperial (American) socket sizes. If the fraction is listed, it's the size of your nut and required socket. If you find no corresponding fraction, your nut and its required socket is sized in metric units.

This link will give you a conversion chart.

http://www.marylandmetrics.com/tech/cvtchtfdm.htm
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