Depends where you are.
A Airline uses...
4 bars = Captin
3 Bars = Senior First officer
2 Bars = First officer
A flying school may use...
4 Bars = Senior pilot (of some type like examiner or head pilot)
3 Bars = Commercial (in a flying school that does com. training)
2 Bars = Qualifed Flying Instructor
1 Bar = Commercial student pilot.
Also "un-qualifed" aviation workers use them to (this gets confusing)..
Airlines use bars to signify
*Operations Officers = thin(1inch) gold stripe
*Operations Assistant= thin gold stripe
*Operations Junior Assistant= thin(0.5inch) gold stripe
*Crewing officers =thin gold stripe
*Crewing Assistant=thin gold stripe
and also engineers wear em to!!
Not sure on the roles each one plays
But they are generally silver and vary between 2inch-1inch.
And the army use em to... Omeegawd,, I am not getting into that one!