This is the cross pin that secures the rear sight block or hinge block onto the barrel on AKM rifles and their derivatives. 
These are made to the original Russian spec and are hardened.

These will fit:

• AKM
• AK-74 and AKS-74u
• AK-100 series
• Tantal
• AIMS-74

They are too short for use on milled pattern guns or RPKs.