These Pratt Dilators are traditionally uterine dilators but are popular for male urethral insertion.  

Solid stainless steel, very heavy they come in a set of eight.  Each end is a different size.  Sizes are French Sizes in 13/15 to 41/43.  French sizes are the distance around the shaft (circumference) in millimeters. This distance can then be converted into the approximate diameter of the sound in millimeters by dividing the French Size by 3. So the diameters of these sounds would be 4.3/5.0 mm to 13.7/14.3 mm.

They come in a handy velvet-lined zippered case for easy storage and transport.