In this diagram

*F*_{h} is the component of the joint reaction force perpendicular to the axis of the screw. The inferior edge of the proximal end of the barrel is the location of the fulcrum in bending. An internal force,

*F*_{b}, from the surface of the barrel acts against the screw to counteract

*F*_{h}. For equilibrium, the moments produced by

*F*_{h} (

*F*_{h} ×

*L*_{e}) and

*F*_{b} (

*F*_{b} ×

*L*_{b}) must be equal. If

*L*_{b}, the distance from the point of application of internal force

*F*_{b} to the fulcrum, decreases,

*F*_{b} must increase to produce the same moment. If

*F*_{b} is larger, the frictional force and therefore the resistance to screw sliding will increase. (

*L*_{e} is the length of the screw beyond the barrel).

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