510 to 510 sealed vs. unsealed?

[micksf]

I want to get some 510 to 510 adapters just so my threads don't get mangled from constant changing of tanks. can anyone tell me what the difference is between sealed and unsealed?

V2 510 Shorty Extension
V2 510 Shorty Extension Sealed

 

[Creniker]

Unsealed will let air reach the original connector, where as a sealed one will prevent liquid or air from getting through the adaptor. If your not using a auto mod, or a bottom feeder I prefer the sealed.