Rings and slides are what those little peanuts are called. They are used to adjust the length of straps and may be placed in either the front or in the back of the bra, depending on how smooth of a look is desired. Most often, they are made of plastic and nylon coated metal and stainless steel and have been known to set off those pesky metal detectors at the airports (“Ms. please step over here for a quick frisk”).
How’s that for quick and dirty?