The Tein Flex Z is a product line that is evolved from the STREET FLEX SF  damper kit system. Historically, FLEX kits from Tein are sets which are readily adapted to many uses, from street to track driving. For the STREET FLEX SF  variant, Tein softed the damping levels and extended stroke range to make the damper kits more tractable for daily use. For many years, Tein product carried the banner of performance value by making damper tubes that could be torn down, overhauled, and re-valved.

As the market evolves with emerging entrants and an increasing need for value, Tein re-designed their popular STREET FLEX SF  line and renamed it the FLEX Z. The "Z-line" moniker has been added to the Street Advance Z and Street Basis Z, and represents a damper tube with similar internal construction as the outgoing overhaul-available "non-Z" product, but a new outer tube which is sealed. Rather than rebuilding worn dampers, users now will simply purchase replacements. 

Newer manufacturing techniques, as well as revised springs that do not need spring seat adapters, allow the new Z-line to come in at a lower MSRP. Tein has literally reset the typical value proposition for assembled full-length damper kit with the FLEX Z. Many users are surprised at the pricing that Flex Z dampers can be had at assuming they are a compromise in quality, or that they are now made in China rather than in Japan. Neither is correct as these parts are still made from scratch in-house by Tein Japan with much of the same internal components that have made Tein products reliable and refined solutions for street-sport applications.

Tein Flex Z offers many features highly valued by users including:
- Twin-Tube System for Comfortable Ride on Streets
- Full-Length System for Ride Height Adjustment w/ Minimal Change in Ride
- Damping Force Adjustable to Change Ride to Desired Settings
- Compatible with EDFC Series to enable In-Car Damping Force Adjustment
- Upper Mounts Included for Easy Installation
- Highly Durable & Reliable
- Thoroughgoing Rust-Proofing
- Smooth Ride Height Adjustment & One-of-A-Kind Adjusting Wrench
- No-Sag Springs
- High-Spec Damper Oil