• Four Wheels: Having four wheels distributes the weight of the door over a larger area, providing increased stability and a higher load-bearing capacity compared to rollers with fewer wheels. This typically results in smoother and easier sliding, especially for heavier doors.
• Adjustable: The inclusion of an adjustment mechanism (usually a screw) allows for fine-tuning the vertical height of the door within its frame. This is crucial for ensuring the door aligns properly with the tracks and seals correctly, especially if there are slight installation variations or building movement over time.
• Groove: The wheels will have a groove (likely V-shaped or U-shaped) that interlocks with a corresponding track. This ensures the door stays on its intended path and slides linearly without wobbling or derailing.
• Application: Primarily used for heavier UPVC sliding doors where stability, smooth operation, and precise alignment are essential.

The use of four wheels suggests a design focused on durability and handling significant weight. The adjustability feature highlights the need for precise fitting in sliding door applications.