The formula Tanb=F/N=μN/N=μ shows that the tangent of the friction angle b is equal to the static friction coefficient. Namely: μ≥ tan θ \ r \ nTangent mapping. \ r \ nThe interval (0, ∞) can be expressed as tan(θ): \r\ntan(θ)=0, when θ=0, \r\ntan(θ)→∞, when θ→90. \ r \ nIf the friction coefficient of the bevel is f=0. 15, and f=0. 15=tan(θ), θ=8.5 degrees, that is, the equivalent friction angle is equal to 8.5 degrees, that is, the self-locking angle is equal to 8.5 degrees, and the thread can be self-locked if the rising angle is less than this angle, otherwise it will be disengaged. \ r \ n \ r \ Thread friction angle: Thread can be regarded as an inclined plane wound on a cylinder, and the principle of inclined plane is applied to thread. When the object is on an inclined plane, the resultant force R of the normal reaction force N and the friction force F is called the total reaction force supporting the object. That is, when the friction force f reaches the maximum value Fmax, the included angle a also reaches the maximum value b, which is called the friction angle.