Constant IV_LEN 

pub const IV_LEN: usize = IvLen::USIZE /* 8usize */;

Size of an AES-KW and AES-KWP initialization vector in bytes.

This value is equal to “semiblock” size. From NIST SP 800-38F § 4.1:

semiblock: given a block cipher, a bit string whose length is half of the block size.