Can you wear a nipple ring if you got it pierced with a bar?

Nipple piercings are straight piercings regardless of what jewellery is in the piercing when it was first done, the barbell allows the piercing to discharge and affords room for cleaning better than a ring does. Don't let anyone tell you that if the piercing is done with a curved needle the piercing is curved, that a line of BS.

Once the piercing is healed you can change over to what is called a "D" ring this ring has a straight section that goes through the piercing and is by far more comfortable than a standard ring. It has the appearance of a ring but the straight segment allows the ring to be moved without twisting a curvature in the piercing like you would with a standard ring. Ultimately for day to day wear the barbell is going to be your jewelery of choice, for comfort and discretion.