Ball-bearing tracks & Traveller car. Tracks are of a hollow section extruded aluminium for lightweight and high load capability. The æSpectroÆ grey anodised finish is extremely durable and adds to the friction free performance of these products. The recirculating ball-bearing travellers run on Delrin ball bearings. Size 2 is for yachts up to 12 meters. Size 3 is for yachts up to 15 meters.