Roller and inverter pulley two design with bearing (recommended for high load size 626 bearing) and without bearing the external dimension between 28 to 38 mm width 16 to 18 mm , hole 6 mm or 19 mm

Top Choice: Carbon Fiber Nylon (PA-CF)Unmatched tensile strength.Resists heavy band tension.High impact resistance.Excellent UV stability.Note: Requires an enclosed printer, hardened steel nozzle, and a drybox.Alternative 1: Polycarbonate (PC)Extremely rigid material.Handles high impact well.Excellent temperature resistance.Note: Prone to warping during printing; requires an enclosure.Alternative 2: PETGEasiest budget material to print.Completely waterproof and chemical resistant.Good UV resistance.Note: Flexes more under load than Nylon or PC; use thicker walls.Material to AvoidPLA / PLA+: It absorbs water, degrades in sunlight, and creeps (deforms permanently) under continuous rubber band tension.Standard ABS: It degrades quickly under UV exposure from the sun and can become brittle in saltwater