The most common rear differential for Chevrolet half-ton trucks, the GM 8.5 inch, appear almost perfectly round when looking at the differential cover, with 10 differential cover bolts. The differential used in a Chevrolet truck varies by year, make and model, and by the included equipment package. Among the most common General Motors manufactured rear differential for Chevrolet trucks are the GM 8.5 inch, the GM 8.6", the GM 9.5 inch, the GM 12 Bolt and the GM 14 Bolt.
All Chevrolet truck rear differentials manufactured after 1965 have a rear differential cover with at least 10 differential cover bolts. The shapes range from perfectly round to something that looks like half a squished football. The GM 14 Bolt, typically used in three-quarter and one-ton trucks, is easily identified by a 6-bolt pinion support on the front of the rear differential. A visual guide to all Chevrolet rear differentials is available at Differentials.com. The website provides a view that is directly facing the differential cover.
To identify the differential used by year, make and model, a differential identification resource such as DiffWizard.com narrows the options based on user input data. After the make, model, year and drive type is input to DiffWizard.com, the available differentials options for that application are returned, with pictures for visual identification.