Rubber bumpers shown in the photo:
Left: 0.44H x 1D inch (1.1H x 2.5D cm)
Center: 1H x 1D inch (2.5H x 2.5D cm)
[Extender for the Tank Brace]
Right: 1.25H x 1.25D inch (3.1H x 3.1D cm)
The standard outside rubber bumpers are 0.44H inch (1.1H cm) on the Tank Brace and do not make contact with the Doubles, due to the static 2 inch (5 cm) distance between tanks.