In 1921, Ernst Dehmel, a German inspector of orchestras and bass trombonist from Berlin, patented a new design of contrabass trombone, utilising the old German military band bass trombone in F, equipped with two independent rotary valves to replace the handle required on the long slide and to fill in the missing notes between the first partial (fundamental) in closed position and the second partial with the slide fully extended. This bass-contrabass instrument is the precursor of the modern contrabass trombone, which is still largely constructed according to the same principles and, to all intents and purposes, completely replaced the older double slide variety, which is very rarely seen today. Bore sizes for the slide of the contrabass trombone are typically in the range; the most common sizes on contrabass trombones in F are between as the larger sizes are usually reserved for the contrabass trombone in low B. The bell diameter is typically .