1. Component Breakdown:

• Residential: Designed for home use (e.g., patio doors, balcony doors) as opposed to heavy-duty commercial or industrial applications.

• Reinforced Glass Sliding Door: These rollers are engineered to carry the significant weight of a large door made with tempered or laminated (reinforced) glass, often within an aluminum or PVC frame.

• Roller Wheels: The core of the mechanism. These are typically made from Nylon or Polyamide (a very durable engineering plastic) and are often reinforced with a glass fiber composite. Higher-end models may feature sealed ball bearings inside the wheel for smoother rolling. The wheel itself is what makes contact with the track.

• Zinc Alloy Housing: The bracket or carriage that holds the wheel. Zinc alloy (like Zamak) is chosen because it is:

  • Strong and Durable: Can withstand heavy loads without bending.

  • Corrosion Resistant: Essential for doors exposed to the elements.

  • Precise: Allows for detailed casting of threads and adjustment mechanisms.

• Screw In: This is the most critical identification feature. It refers to the height adjustment mechanism.

  • A large, vertical screw (usually a hex/Allen key bolt) is located on top of the housing.

  • Turning this screw raises or lowers the entire roller assembly, which in turn lifts or drops the door within its frame.

  • This adjustment is used to align the door, compensate for a sagging door, or lift it clear of the threshold for easy removal or cleaning.

2. Key Identification Points (Before You Buy):

To ensure you get the correct replacement, you MUST identify these three things on your old roller:

1. The Housing Style & Screw Location:

   • "Screw-In" (Top-Adjusting): The adjustment screw is on the top of the housing. This is the type your description matches.

   • "Side-Adjusting": The adjustment screw is on the side of the housing. They are not interchangeable.

2. Dimensions (Crucial!):

   • Wheel Diameter: Measure the old wheel's diameter (e.g., 35mm, 40mm, 45mm).

   • Overall Height: Measure the height of the entire roller assembly from the bottom of the wheel to the top of the housing.

   • Housing Width: Measure the width of the metal housing that slots into the door frame.

3. Weight Capacity:

   • Most rollers are sold in packs of 2 or 4. Check the rated capacity per pack (e.g., "Set of 4, holds up to 200 lbs / 90 kg"). Ensure this is adequate for your door's weight.

3. Symptoms You Need to Replace Them:

• The door is hard to push or pull.

• The door wobbles or feels unstable.

• The door has dropped and is scraping along the bottom track.

• You hear grinding, cracking, or squeaking noises when operating the door.

• The wheels are visibly cracked, flattened ("flat-spotted"), or have disintegrated.