Internal diameter (ID): 12,5mm (1/2\") Outer diameter (OD): 19,4mm (3/4\")EK ZMT (Zero Maintenance Tubing) is a high quality, zero maintenance, industrial grade EPDM rubber tubing in stylish matte black.This tubing is - just like Norprene - designed to withstand harsh conditions for a very long period of time, offering a truly exceptional lifespan even under UV, ozone and heat exposure for many years.Unlike most PVC and PUR tubing this high quality EK made EPDM rubber tubing ensures long lasting operation and does not suffer from a plasticizer leaching effect which can cause blockage (gunking) in your liquid cooling loop. This 12,5/19,4mm (ID/OD) tubing also allow for very small bend radius!This may not be the tubing for everyone, but it is guaranteed to be hassle-free even in the long run which is something other PVC/PUR tubing cannot offer!This tubing is a perfect companion for EK-ACF Fitting 13/19 series compression fittings.Technical specifications: - Material: EPDM- Color: Black, not UV-reactive- Outer diameter: 19,4mm (3/4\")- Inner diameter: 12,5mm (1/2\")- Operating temperature range: -30C to 110C- Compatible with all known widely used coolants