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4 Types of Internal Splines That Almost Every Machine Needs

June 03, 2021

4 Types of Internal Splines That Almost Every Machine Needs

Internal splines are needed for many types of engines or machines. They insert into another shaft's slot and their grooves get locked together, allowing them to transfer torque smoothly with reduced vibration. This convenient, space-saving, and efficient system has wide usage in engine manufacturing.



Here are four types of internal splines that virtually every machine and engine needs:




These internal splines are shorter than average splines, allowing them to deliver higher strength and torque levels to machines. In addition, they save space in most mechanical designs. Involute internal splines ensure smooth torque transition through a radius, and it comes in several varieties:

  • Flat Root Side Fit
  • Fillet Root Side Fit
  • Major Diameter Fit


Parallel Key

If you've used a keyway drive before, parallel keys are another variety that uses the same design and torque-delivering principles. It has straight-sided, equally-spaced teeth. Their main difference with keyway drives is their keys are much more crucial to the shaft with equal circumference spacing, allowing them to deliver torque through a shaft.



This internal spline is a variation of the involute type. Angular misalignment between the shaft and insertion port plays a crucial role in penetration and torque locking, allowing it to deliver higher strength levels. The crowning process allows the internal spline to achieve this objective effectively.



Like their helical gear counterparts, helical splines use a lead and helix angle shaft. Typical shaft splines can get wound up to the point of breaking. Helical splines can share a load with parallel splines, reducing torsional forces that can break a typical internal spline apart.


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