Transmission fluid lines (commonly called transmission cooler lines or fluid tubes) carry automatic transmission fluid (ATF) between the transmission and the external cooler (radiator or dedicated cooler). They allow heat exchange to keep ATF within safe operating temperature and enable fluid flow for lubrication, hydraulic actuation, and torque converter operation.

The development of tranny tubes dates back to the early days of transistor technology. In the 1950s and 1960s, transistors were still relatively expensive and not widely available. To meet the demand for more affordable and reliable transistors, manufacturers began encapsulating transistors in glass tubes, which provided a protective environment and made them easier to handle.

: "Modding" or repairing gear often involves replacing both the transformers ("trannies") and the tubes to achieve a specific tone or to fix damage caused by impedance mismatches. The Importance of a Tranny Tube by nahid888 on DeviantArt

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: Improper installation can restrict flow, causing immediate pressure spikes and heat buildup. Rubbing/Chafing

: Standard steel tubes are prone to rusting, especially in "salt belt" regions, which can lead to fluid leaks or debris entering the transmission. Seal Failure

Unlike rigid factory pipes, these are made of braided stainless steel. They are popular for: