De manera que tu frase quedaría de la siguiente manera:

"Los tres platos de fricción OD encajan mediante ranturas al cilindro del embrague de inercia"

Mira la definición de spline aquí:

http://driving.50megs.com/a_z/s.htm

• Spline

In order to secure one object on a shaft, longitudinal grooves or splines are cut all around the shaft with matching grooves in the object. In this way the object slides on the shaft for installation so that both the object and the shaft rotate together.

Usando el operador "Define" de Google encontrarás, entre otras, las siguientes definiciones: (Define:spline)

A ridge on a surface of a part, usually used to prevent an otherwise circular part from turning. Commonly used on freewheels and cassettes where the sprockets attach. Some frame tubing has internal ribs to reinforce the tube, these are sometimes also referred to as splines.
www.sheldonbrown.org/gloss_sp-ss.html

Any of a series of projections on a shaft that fit into slots on a corresponding shaft.
inventors.about.com/library/inventors/blrailroad6.htm

A feature of parts that allows two shafts to be connected. This connection is very resistant to applied torque ant still allows for adjustment in the parts axial position.
ourworld.compuserve.com/homepages/MJVanVoorhis/T550.htm

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Las definiciones que anulé de spline se refieren a métodos de interpolación matemática (más 15 definiciones) y a trabajos de madera (3 definiciones) Las 3 que he dejado aquí son las aplicables a tu caso.