The TSO, Tourist Second Open, became the most common type of second or standard class coach from the 1970s. Seating was arranged with four seats around a table, each table lined up with a window, the 8 bays providing 64 seats. The arranagement with two seats each side of the central aisle, known as a 2+2 arrangement. The SO coaches had a 2+1 arrangement, with a row of single seats/tables along one side, providing just 48 seats and these coaches were intended to serve as second class dining saloons, similar to the RFO type first class coach.
TSO remains the most commn type of coach in service, though seat spacing reductions to increase capacity often means the table don't line up with the windows any more.