M8 1.25 1.5D (5PCS). M8 1.25 3D (5PCS). M6 1 1.5D (10PCS). - Due to a certain elasticity, the thread rt can balance the load distribution on each thread, eliminate pitch and tooth deviation between screw and screw hole, and absorb vibration, thereby increasing screw thread connection strength and fatigue resistance.
eBay