BKCJ – 0361 – 13 tooth, XD15 Ceramic Hybrid Bearing, Machined Delrin Derailleur Pulleys for 12 speed Shimano XTR and XT Derailleurs (5mm bolt hole) The ultimate upgrade pulley. Guaranteed to last forever against corrosion Precision machined Delrin Derailleur pulleys featuring XD15 Ceramic – Hybrid, radial bearings for enhanced shifting performance and longevity. Designed and manufactured for performance, these pulleys feature CN (tight clearance) bearings in the upper pulley to maximize shifting accuracy and C4 (loose clearance) bearings in the lower pulley to allow for chain – line movement. 500 AF Delrin pulley material features a high mechanical tensile strength and rigidity, natural lubricity, high resistance to moisture, caustic chemicals and UV makes these pulleys highly durable, rigid and very smooth. Delrin also machines very cleanly and precisely. The inherent lubricative qualities of this Teflon – infused material greatly reduces friction when it interfaces with the bicycle chain. When compared to other pulley materials, 500 AF Delrin with Teflon, offers significantly less drag than pulleys machined from aluminum or titanium. An Enduro Bearings exclusive, our XD15 Ceramic – Hybrid bearings combine corrosion – proof, cryogenically treated nitrogen steel races with Silicon Nitride Grade 3 ceramic balls in a proprietary process that results in the ultimate high performance bearing setup. The deep – groove design raceways allow for maximum sized Grade 3 Silicon Nitride ceramic balls for for increased contact area and improved performance and longevity. 90% fill Kluber NBU52 grease only runs better and smoother with time and is highly resistant to being washed out. It is engineered to stick to the balls and continually be pulled back into the ball path where it is needed., The eleven tooth upper and 12 tooth lower size and profile with 5mm bolt – holes are designed as an upgrade for most 12 speed Shimano XTR and XT Derailleurs (5mm bolt hole) Enduro Derailleur Pulleys are available in a number of configurations and performance levels and are all are proudly precision manufactured in the USA.