Lock cylinder differences?

[79BIG10]

I was looking at getting 2 new sets of locks for the truck and blazer but I saw that the cylinders are different on 73-78 and 79-87. What are the differences? Reason I ask is the column in the truck was rebuilt and was a bolt in no problem but not sure what year it was. Then the blazer may need a new column and I don't want to order a set that may not fit if the new column is a different year than the set I buy. Anybody know the differences and how to check without tearing the new column of mine apart?

[beaterC10]

The difference is in the way the cylinder is retained in the column. The later ones use a screw the earlier ones don't. The later columns also had double flats on the end of the steering shaft, the earlier ones were splined.

I don't know if these two features changed at the same time, so this may not be a completely foolproof way to id the column. To look at how the cylinder is retained youi need to remove the wheel, lockplate and the screws that hold the turn signal switch in.

[79BIG10]

Thanks for the info. I'll have to tear into both of mine then to find out which I need once I get the Blazer's column fixed/replaced.