For the T-bond contract, any Treasure bond that has at least 15 years to the nearest call date or to maturity (if non-callable) can be used for delivery.

对于国债期货，任何距最近的赎回日或到期日（假如不可赎回）长达至少15年的国债可用于交割。

youdao

High Yield bonds are usually non-callable for about half of life of the bond;

高收益债券通常在期限过半时不可赎回；

youdao

One, the yield to the worst call date is much better than yield to maturity of a non-callable bond (aka, bullet bond).

FORBES: Don't Hate All Bonds, Buy Yield To Call Paper