A matched pair of spiral bevel gears always has opposite spiral directions — one right-hand (RH) and one left-hand (LH). If the pinion is right-hand, the gear must be left-hand, and vice versa. The spiral direction determines thrust load direction and which bearing takes axial load. To specify correctly, stand behind the pinion and look toward the gear. If the spiral teeth lean to the right as they go away from you, the pinion is right-hand. If they lean to the left, it is left-hand. For standard reducer layouts, the pinion is typically right-hand, but you should always check your existing gear or assembly drawing. If you are unsure, do not guess — send us a photo of your old gear set or the assembly drawing. We will confirm the correct pair for you. Specifying the wrong direction will cause improper thrust loading, overheating, and rapid failure. When in doubt, ask us — we are happy to help you get it right.