Replacement Sealing O-rings. 
One replacement set of (2) Vinton O-rings for 2 Stroke pipe collar.
Fits pipe collar pn#  EC-BETA
Fitment From Parts Finder:
BETA  (15-18) 250 /300 2 Stroke & 300 X-TRAINER   
OEM & FMF PIPE & Turbine core 2 SILENCER
  Not the Turbine core 2.1
       
         
        
          Replacement Sealing O-rings. 
One replacement set of (2) Vinton O-rings for 2 Stroke pipe collar.
Fits pipe collar pn#  EC-BETA
Fitment From Parts Finder:
BETA  (15-18) 250 /300 2 Stroke & 300 X-TRAINER   
OEM & FMF PIPE & Turbine core 2 SILENCER
  Not the Turbine core 2.1