No such thing as a dead zone. You turn down the smallest size that is larger than the diameter you need. Only turn down the length you need so you'll eventually end up with stepped mandrels. There is a seller on eBay (factory, I assume) that seems to sell all Breakheart lathe accessories. The seller name is
thirdwheelrider. I keep spares on hand (you know why). Looks like eBay is free shipping on that set. Sorry about that. I didn't think about eBay 'till just now. Also, import clones on eBay for less $$, but I can only guess as to quality. Breakheart = USA made and no problems.
Disclosure: No connection with Breakheart. Just a satisfied customer.