Carriage type BSO (Brake Standard Open) designates a carriage with a Guards's compartment, together with open seating around tables for second (later standard) class passenger use.
Following the introduction of TOPS in the late 1960s, BR carriages of this class were allocated the [[TOPS code]] '''AE21''', denoting:
A: Passenger carrying stock<br>
E: Gangwayed open brake<br>
2: Second (later standard) class<br>
1: BR Mark 1 carriage
==See also==