C.S. Osborne 3/4" Brass Plain Rim Ventilators. One-piece construction for added strength. Used as breathers for mattresses, cushions and plastic slipcovers. These ventilators are set with CS Osborne No. 621-3/4 Ventilator Setter and can be also set using Osborne Hand Press W-1 & Pneumatic Machine W-3 with the ventilator dies. Size : 3/4" (Osborne No. V-1 3/4) Diameter of hole when set : 9/16" Packed one gross