The B-26 is a picatinny-mounted firing mount adapter for PK, PKM, and PKP machine guns.

It is mounted on the B-50 handguard (which blocks access to the standard firing mount adapters on the machine gun) directly under the standard mount adapters located under the barrel. 

Allows the machine gun to be reliably mounted to tripods, various firing stands, and mounted to PK/PKM/PKP compatible vehicle machine gun mounts.

B-26 Firing Mount Adapter