O-ring,Viton,16.5 x 3 mm

This is a circular rubber ring. It measures 16.5 mm on the inside (that is the hole in the middle). The rubber itself is 3 mm thick. You will often see this size written as 16.5 x 3. It fits into a groove between two metal parts. When you tighten the parts together, the ring gets squished just a little. That squish creates an airtight seal 

This ring is made from Viton, which is a brand name for FKM rubber . Regular rubber cannot handle the heat inside a working pump. It gets hard and cracks. It also swells up when it touches oil.

Viton is different. Here is what makes it special:

• Heat resistant: It works in temperatures from about -15°C up to +200°C (that is 5°F to 392°F) .

• Chemical resistant: It stands up to oils, fuels, solvents, and many acids .

• Long lasting: It resists ozone, weather, and aging. It does not crack or dry out easily