A bibb washer is generally made of neoprene and comes in three different styles. These styles include flat, beveled and swivel-head.
Both the flat and beveled styles are held to the stem of the faucet by either a brass or monel machine screw. A swivel-head bibb washer is held to the stem of the faucet by prongs in place of screws.
A bonnet washer is made of cloth-inserted rubber. Bonnet washers are typically flat washers and are used to stop any leakage that may occur between the faucet bonnet and body of the faucet.
Rubber Gasket Washer
Rubber gasket washers are commonly employed in faucets to prevent leakage by stopping the water flow in a particular direction. A rubber gasket can either be flat or partly beveled on one of the sides of the washer.
Both serve the same function of sealing up the barrel in the valve's faucet.