Why 3 inch vs 2 1/2 inch half shafts?

[Brassplyer]

I've been told that the 2 1/2 inch shafts are actually stronger than 3 inch shafts.

Why were 3 inch shafts used?

 

[Tuna]

I thought the bigger, 3-inch half-shafts were used on big block cars to handle the higher torque they could put out.

 

[ratflinger]

A 3" tube is inherently stronger than a 2.5" tube

 

[douglasamariani]

Whoever told you that the 2 1/2 inch shafts are actually stronger than 3 inch shafts is wrong.