Form Circle is the circle which defines the deepest points of involute form control of the
tooth profile. This circle along with the tooth tip circle (or start of chamfer circle) determines the limits of tooth profile requiring control. It is located near the major circle on the
internal spline and near the minor circle on the external spline.
Form Clearance (cF) is the radial depth of involute profile beyond the depth of engagement with the mating part. It allows for looseness between mating splines and for eccentricities between the minor circle (internal), the major circle (external), and their respective
pitch circles.
Form Diameter (DFe, DFi) the diameter of the form circle.
Internal Spline is a spline formed on the inner surface of a cylinder.
Involute Spline is one having teeth with involute profiles.
Lead Variation is the variation of the direction of the spline tooth from its intended direction parallel to the reference axis, also including parallelism and alignment variations (see
Fig. 1a). Note: Straight (nonhelical) splines have an infinite lead.
Length of Engagement (Lq) is the axial length of contact between mating splines.
Machining Tolerance (m) is the permissible variation in actual space width or actual
tooth thickness.
Major Circle is the circle formed by the outermost surface of the spline. It is the outside
circle (tooth tip circle) of the external spline or the root circle of the internal spline.
Major Diameter (Do, Dri) is the diameter of the major circle.
Minor Circle is the circle formed by the innermost surface of the spline. It is the root circle of the external spline or the inside circle (tooth tip circle) of the internal spline.
Minor Diameter (Dre, Di) is the diameter of the minor circle.
Nominal Clearance is the actual space width of an internal spline minus the actual tooth
thickness of the mating external spline. It does not define the fit between mating members,
because of the effect of variations.
Out of Roundness is the variation of the spline from a true circular configuration.
Parallelism Variation is the variation of parallelism of a single spline tooth with respect
to any other single spline tooth (see Fig. 1b).
Pitch (P/Ps) is a combination number of a one-to-two ratio indicating the spline proportions; the upper or first number is the diametral pitch, the lower or second number is the
stub pitch and denotes, as that fractional part of an inch, the basic radial length of engagement, both above and below the pitch circle.
Pitch Circle is the reference circle from which all transverse spline tooth dimensions are
constructed.
Pitch Diameter (D) is the diameter of the pitch circle.
Pitch Point is the intersection of the spline tooth profile with the pitch circle.
Pressure Angle (φ) is the angle between a line tangent to an involute and a radial line
through the point of tangency. Unless otherwise specified, it is the standard pressure angle.
Profile Variation is any variation from the specified tooth profile normal to the flank.
Spline is a machine element consisting of integral keys (spline teeth) or keyways
(spaces) equally spaced around a circle or portion thereof.
Standard (Main) Pressure Angle (φD) is the pressure angle at the specified pitch diameter.
Stub Pitch (Ps) is a number used to denote the radial distance from the pitch circle to the
major circle of the external spline and from the pitch circle to the minor circleof the internal
spline. The stub pitch for splines in this standard is twice the diametral pitch.
Total Index Variation is the greatest difference in any two teeth (adjacent or otherwise)
between the actual and the perfect spacing of the tooth profiles.
Total Tolerance (m + λ) is the machining tolerance plus the variation allowance.
Variation Allowance (λ) is the permissible effective variation
