Slope — The Flat-Taper Ratio Callout

The slope symbol before a ratio states the inclination of a flat surface — the height difference between its ends divided by their separation — the flat-taper counterpart of the conical taper callout.

Definition

Slope is the inclination of a surface expressed as the ratio of the difference in the heights at each end — measured above and at right angles to a baseline — to the distance between those heights: slope = (H − h)/L. The symbol precedes that ratio as the dimension. Where conical taper controls a surface of revolution, slope controls a flat surface: a wedge, a ramp pad, a tapered keyway seat.

Why the slope value is commonly basic

The slope value depends on the height and length dimensions from which it is calculated — it is derived geometry. Box the slope ratio as a basic dimension and let a geometric control (profile or angularity) govern the surface; that keeps one authority over the inclination. If the slope is directly toleranced instead, the standard's angular-surface rule applies: a linear dimension combined with the angular dimension produces a zone of two nonparallel planes that widens with distance from the apex — legal, but a profile or angularity control is the way to get parallel boundaries.

Specifying a flat taper

A flat taper may be specified by a toleranced slope and a toleranced height at one end: the slope ratio fixes the inclination, the height fixes where the surface sits, and together they locate and orient the plane. The geometric alternative trades the pair of size tolerances for a basic slope plus a profile or angularity control. The symbol is the open right triangle, vertical leg to the left — the closed triangle belongs to conical taper. Read them as a pair: same grammar, one for cones, one for flats.

• Toleranced slope + toleranced height at one end — the standard's direct method (Figure 5-23)
• Basic slope + profile of a surface — parallel zone boundaries, one geometric authority
• Basic slope + angularity — when orientation to a datum matters more than the surface's exact form
• Directly toleranced slope + height alone — legal, but the zone becomes two nonparallel planes that widen away from the apex