Tim:

There are two adapters necessary to use the Stant Cooling System 
Tester:  one is the Audi/Volkswagen System Adapter (Stant P/N 
12016 {old Stant P/N TA-16}) which will allow you to test the 
cooling system itself.  The other is the Audi/Volkswagen Cap
Adapter (Stant P/N 12017 {old Stant P/N TA-17}) which will allow
you to test the expansion chamber cap. 

The best prices I have found on these adapters has been an auto
parts house in Santa Clara California.  I have included a series 
of equivalent part numbers and venders below.

Vender          System Adapter   Cap Adapter
 APS              46810            46811
 Carquest         46810            46811
 Dayco            85516            85517
 Federated        46810            46811
 Napa Balkamp     700-1305         770-1306
 Parts Master     46810            46811
 Pronto           46810            46811
 Robertshaw                        RTA 17
 Rockhill         46810            46811

Hope this helps.

Fred
84 Vanagon