Analysis of information sources in references of the Wikipedia article "Spline (mechanical)" in English language version.
1966 G. W. MICHALEC Precision Gearing vii. 324 Generally, involute internal and external teeth are mated, but non~involute splines are also suitable. 1979 Industrial Fasteners Handbk. I. 318 There are two basic forms of spline--straight-sided splines which may number 4, 6, 10 or up to 16 splines equally distributed around the circumference of a shaft, and serrated splines which are in the form of adjacent triangular teeth.
The externally splined shaft mates with an internal spline that has slots, or spaces, formed in the reverse of the shaft's teeth.
