Guarder Bore-Up Air Seal Nozzle For AK Series Airsoft AEG

"Good nozzle, but make SURE your cylinder head is designed for bore-up kit! VERY IMPORTANT!

Install this into a regular system, you will get air leak.
Install this into a bore-up system, you will get good air seal.
Simple as that.

However, the inner o-ring is somewhat on the down side, it isn't that great even it was lubed with pure silicone oil.

On the bright side, the o-ring is pretty easy to change.