Full Colour Diffuser Downstem. These colored downstems have cuts at their ends to diffuse the smoke as it enters your bong. Joint Size: 19mm Male / 14mm Female Lengths: 4" or 10cm / 4.75" or 12cm / 5.5" or 14cm / 6.25" or 16cm Full Colour Diffuser Downstem. These colored downstems have cuts at their ends to diffuse the smoke as it enters your bong. Joint Size: 19mm Male / 14mm Female Lengths: 4" or 10cm / 4.75" or 12cm / 5.5" or 14cm / 6.25" or 16cm