Heavy duty metal construction for protection and compatibility Built to be compatible with E&L M4 / M16 AEGs and most M4 / M16 platform AEGs Standard version 2 design Quick change spring guide system Reduction of shell thickness for greater compatibility with most M4 / M16 receivers In the Box 1X Gearbox Shell Specifications: Brand E&L Airsoft Build Metal Compatibility E&L M4 / M16 AEGs and most M4 / M16 platform AEGs Color Black California Proposition 65 Warning: Cancer and Reproductive Harm - www.P65Warnings.ca.gov