Here’s a breakdown of their characteristics:

• Two Flat Wheels: The key feature is having two separate wheels with flat outer surfaces that contact the track.
• Increased Stability: The dual contact points offer more stability, helping to prevent wobbling of the sliding sash.
• Higher Load Capacity: Two wheels can generally support more weight than a single wheel of a similar size.
• Smoother Operation: The distribution of weight over two points can sometimes result in smoother gliding.
• Material: The wheels are typically made of nylon or other durable plastics. The frame or housing holding the two wheels can be made of metal or plastic.
• Application: Used in sliding UPVC windows and doors where the track is flat and where more stability or load capacity is needed.