CowCow Upper Lock for Action Army AAP-01 - Airsoft Extreme
The Otis Technology AR-15 Lock Block | PRO+ AR-15 Lock Block - Upper Receiver Vice Block | Made in the USA
Amazon.com: Child Proof Door Top Lock - Loswsdg Kids Safety Door Lock Made of Durable Metal - Adjustable Sliding Top Door Lock for 0.6-2.2" Thick Doors - Can Open Door from Both
G-Tel Enterprises > Parts > Medco Upper Lock & Key Set
CowCow Upper Lock for Action Army AAP-01 - Airsoft Extreme