The item description is as follows:
Helmet, Light Weight, HGU-55/P with MBU-20P Configuration, High Speed Visor, Anti-Friction Strip and Receiver Spacer.
National Stock Number (NSN):
8475-01-542-2592 (Size Medium)
Part Number 81D5330-13 (Cage 97427)
8475-01-542-2603 (Size Large)
Part Number 81D5330-14 (Cage 97427)
84754-01-542-2612 (Size X-Large)
Part Number 81D5330-115 (Cage 97427)
This is an Air Force Designated Critical Safety Item (CSI).
Helmet, Light Weight, HGU-55/P with MBU-20/P Configuration, Standard Visor
National Stock Number (NSN):
8475-01-542-2562 (Size Medium)
Part Number 81D5330-16 (Cage 97427)
8475-01-542-2571 (Size Large)
Part Number 81D5330-17 (Cage 97427)
8475-01-542-2576 (Size X-Large)
Part Number 81D5330-18 (Cage 97427)
This is an Air Force Designated Critical Safety Item (CSI).