The Sigma MC-21 Adapter Lock secures the MC-21 L to EF adapter to the XLCS Cage, eliminating potential mounting failures and relieving strain on the native mount. Machined from high-strength aluminum and anodized black, it is specifically designed for the MC-21 Adapter from Sigma--and is the cleanest way to adapt lenses to your Sigma FP or FPL.
 
Also Compatible with PYXIS 6K Full Metal Jacket.
 
FOR VILTROX/METABONES ADAPTERS, PLEASE SEE THE METABONES SPECIFIC LISTING
 
Includes: Adapter Lock, Mounting Screws and Hex Wrenches