The JB Unicorn 6.75in MSS(Modular Suppresor System) Barrel Extension kit has some interesting features: 

JBU (MSS) Modular Suppressor System   
Aluminum Alloy Construction
14mm Counter Clock Thread Flash-hider
6.75in x 1.5in dimension 
4pc Set, includes Flash-hider  
Unique JBU Serial Number  
Fits All 14mm CC Thread Airsoft AEGs 

JBU 6.75in x 1.5in, Modular Suppressor System, Includes Aluminum 2pc Long Version & QD Steel Phantom flash hider.  Constructed with High Strength Aluminum Alloy and Unique Serial Number, (5pc Set) includes: barrel cap, forward extender, base extender, flash-hider adater, & flash-hider.  

*Note:  This Barrel Extension system has no silencing capability and is for replica/cosmetic purposes only.  Any modification of this product for uses other than airsoft play may violate local and Federal law.