The 
VORSK 11" V-Rail System & Barrel Nut (VMP-2M)
 uses a GBB AR15 specification barrel nut, which is a proprietary part from VORSK, not a universal standard. 
 
VORSK VMP-2M Barrel Nut Details
Compatibility: The rail system is designed to be compatible with GBB AR15 spec components, including the handguard, grip, and stock tube, but the barrel nut itself is a specific VORSK part for the VMP-2M and VMP-2MD models.
Material: The original barrel nut is made of steel.
Availability: The barrel nut is typically included when purchasing the complete V-Rail system. It can also be purchased separately as a spare part directly from VORSK retailers.
Installation: Installation requires specific alignment with the VMP-2M upper receiver for a secure and stable fit. 
 
It is recommended to purchase the official VORSK replacement part to ensure proper fit and function with the V-Rail system and the VMP-2M's alloy receiver.