Plugs can be worn in any piercing if the wearable length is sufficient for the piercing in question. Typical lengths are 5/16 to 7/16 , but can be custom made to other specifications. Plugs can be hollow, solid, or anything in between, and come in nearly every material used in the market today. Sizes are commonly 10g and up, but smaller sizes can sometimes be found. Plugs are generally held in place by flared or threaded ends, or rubber or silicone o-rings.
Images to the right are idealized versions of various plug types.