Locking parts by static friction (adherence): screwed assembly.
Free body diagram of the top part:

F→1{\displaystyle {\vec {\mathrm {F} }}_{1}} : external action;
F→2{\displaystyle {\vec {\mathrm {F} }}_{2}} : action of the screw on the top part (through the washer);
F→3{\displaystyle {\vec {\mathrm {F} }}_{3}} : action of the support on the top part.The locking works as long as F→3{\displaystyle {\vec {\mathrm {F} }}_{3}} says inside the static friction cone, i.e. as long as ‖T→‖{\displaystyle \|{\vec {\mathrm {T} }}\|} is smaller than μ×‖N→‖{\displaystyle \mu \times \|{\vec {\mathrm {N} }}\|} where

T→{\displaystyle {\vec {\mathrm {T} }}} is the tangent component;
N→|{\displaystyle {\vec {\mathrm {N} }}|} is the normal component;
μ is the static friction factor;
μ = tan φ
Own work
Cdang