Delta towing frame
A delta towing frame is a special form of a one or two-axle Bissel frame , which is used in particular in steam locomotives with a tender as a trailer or towing frame . The Delta towing frame carries the standing boiler, which can be arranged behind it unhindered by the coupled wheel sets. In order not to obstruct the ash pan, the frame has externally mounted wheel sets and a characteristic triangular shape that is reminiscent of the Greek letter Delta and thus led to the name. Frames made of cast steel are typical, particularly for North American locomotives and the designs they influence.