VEXpro Timing Pulleys - VEXpro 217-4100, VEXpro synchronous timing belts are lighter and more efficient than chain. Once set up, they require no tensioning or adjustment.The HTD profile is ideal for FIRST ® Robotics Competition applications - its deep tooth profile allows it to better handle high reversing loads, such as those found in an FIRST ® Robotics Competition drive-train. Each year, more and more FIRST ® Robotics Competition teams make the design switch to belts and attain superior performance. VEXpro 217-4100 Timing Pulley HTD 5mm 18T 15mm Wide Aluminium 1/2\" Hex Bore