These are complete bolt assemblies that are proprietary for the SR-15/SR-16 E3 IWS with rounded locking lugs.
The bolts are slightly used but have been fully QA'd and rebuild as necessary, we'll give you one guess as to where these most likely came from. 
Includes a complete bolt with extractor, ejector and gas rings.  Chrome plated.
These are not a production items so supplies are limited, we reserve the right to limit quantities per customer.  
NOTE: Will not fit in any gun/barrel other than Knight's Armament SR-15 with E3 barrel extension.  Will not work a standard AR-15 barrel.