quickieaircraft

Those must be two different parts. The hole is bigger on the shiny scratched one. I have heard good and bad things about shot peening (bead blasting). It creates a surface layer than has compressive stresses and resists crack propagation (good), but I seem to recall that bead blasting can also hide cracks in aluminum because it can "smoosh" the crack closed (bad). Some more info in http://www.metalimprovement.com//premium/PDF/greenbook_v9/english/MIC%20Green%20Book%20-%209th%20edition%20-%20Complete%20Book.pdf -Emron