CREATE TABLE table_2155350_2 (capacity__litres_ VARCHAR, cab_size VARCHAR, category VARCHAR)

Name the capacity for single cab size 2 medium tanker
SELECT capacity__litres_ FROM table_2155350_2 WHERE cab_size = "Single" AND category = "2 Medium tanker"
SELECT "capacity__litres_" FROM "table_2155350_2" WHERE "2 Medium tanker" = "category" AND "Single" = "cab_size"