Topic: Message #734718

[emsvitil]

BS means British Standard O-ring.

http://www.polymax.co.uk/acatalog/NBR_O-Rings_BS102_-_BS178.html

http://www.polymax.co.uk/Catalogue%20Product%20Pages/02%20O%20Rings%20Pages/O%20Rings%20BS102-BS178.htm

or  ID 1/8   OD 5/16

Then try McMaster Carr........