Stover /Prevailing torque nuts(NUT916) These are metal and have a conical top and a flat bottom bearing surface with chamfered corners. The locking action is created by controlled distortion of their top heads. Their cone shape enables orientation during automated assembly, which is why they're a popular choice for high-volume applications. They're available without flanges, but it's the flange that provides the more secure hold. Even though these are considered lock nuts, they are not permanently locked, which means maintenance or making adjustments can be carried out.