How does it meant to stop from derailing? There’s a stop on the top rail but not on the bottom and it keeps falling forward when pull out…

The SDS London Pull-Out Runner (code 80752) is designed to prevent derailing through a combination of features:

Dual Mounting System:

The runner employs both base and top mounting, ensuring that the weight is evenly distributed and securely supported, minimizing the risk of misalignment or derailing.

High-Quality Ball Bearing Rollers: 

The base runner incorporates plastic-coated ball bearing rollers, providing smooth and controlled movement. This design helps maintain alignment and reduces friction, which can otherwise lead to instability. 

Heavy-Duty Capacity: 

With a carrying capacity of up to 170 kg, the runner is built to handle substantial loads without compromising on performance, further enhancing its resistance to derailing underweight stress. 

These design elements collectively contribute to the runner's ability to maintain proper alignment and prevent derailing during operation.