Your die may be fine, I didn't have to use a reduced diameter every time they called it out, however, they are calling it out so you don't damage the part as there may be a slight curve from the forming process.
Edit: Kind of like fluting if you deform that curve accidentally with a die it could twist the skin.
#140376 RV-14A QB IO-390 Thunderbolt
Progress: All Kits Done
Last edited by bkervaski : 02-12-2018 at 04:40 PM.