The Bitspower Pre-bent 90-Degree Acrylic Hard Tube with an outer diameter (OD) of 16mm likely has an inner diameter (ID) of 12mm. This inference is based on similar products, such as the EK-Loop Hard Tube 16mm, which features a 16mm OD and a 12mm ID.
Additionally, Bitspower's 14mm OD acrylic tubes have an 11mm ID, suggesting a consistent 3mm wall thickness across their products.
Therefore, it's reasonable to deduce that the 16mm OD tube also has a 12mm ID.
For precise information, it's advisable to consult the product's official specifications or contact Bitspower directly.