Each brass (with chrome plating) urethral sound in the series is slightly larger than the one before, and slightly larger on one end than on the other, for a total of 16 graduated sizes in 8 instruments. Diameters range from just over 3/16 inch to about 1/2 inch in diameter. The original intended medical use for these probes was to dilate the cervix, but they are also used to clear blockages in the urinary tract. The tubes are rounded at each end, and they come in a high-quality, zippered leather case (dark brown) with red velvet lining on the inside. This set of 8 inch probes is made of stainless steel.