The Colt OEM Series offers a no-compromise solution for consumers to build customized rifles based on the proven Colt M4 Platform. Handguards, Buttstock, Trigger Guard, Magazine, and Rear Sight have been omitted completely. The OEM1 is ready to accept most aftermarket Drop-In style Handguards that utilize the factory barrel nut and retaining ring. Also Available with Low Profile Gas Block and without Handguard Retaining Ring.