A bra extender is a detachable bra closure that hooks onto the hook and eye closures of a bra to extend the length of the band. They are typically used for comfort, for example a women who is pregnant or nursing may have her body fluctuate in size day-by-day, or they may be used to wear a bra that is too small in the band until it stretches out after a few wears.
Basque and long line extender[]
Basques and long lines can have anywhere from 4 to over 13 hooks. Using an extender may allow for a more customized fit.
Low-back extender[]
A low back extender has the hook and eye closures on the ends of a very long strip of fabric, designed to make a bra 'invisible' when wearing low-back dresses and tops.
Low-back extenders tend to cut into the fat around the torso, and can give a lumpy look under fitted clothing. They can also cause the straps to end lower on the back, which can be a problem for people with low-set breasts and others that need full extension of their bra straps in order for it to fit correctly.