The Van Buren Urethral Sound / Dilating Bougie (8 Charr, 27 cm / 10 ¾ inches) is a very thin, small-caliber urological instrument designed to carefully bypass and gently dilate highly restricted, narrow urethral strictures before larger sounds are introduced.

The term "Charr" or "Charrière" is the historical and technical name for the French gauge (Fr) system.