Rod Joints

About this unit

Rods that carry axial pull or push, such as tie rods, piston rods and valve rods, often need to be joined in a way that can be dismantled. Cotter joints do this using a tapered wedge called a cotter. This unit covers the sleeve and cotter joint for round rods and the gib and cotter joint for square rods, drawn as assembly drawings in two views.

Key ideas

• A cotter is a flat wedge-shaped piece with a small taper on one edge, driven through slots in the parts.
• Cotter joints carry axial tensile or compressive loads, not torque; they are not used to join rotating shafts.
• Slots are made with a small clearance so that driving the cotter draws the parts tightly together.
• Rod ends are enlarged to make up for the material removed by the slot.
• A gib is used with a cotter to give parallel bearing surfaces and to hold the strap or socket together.

How to prepare

Learn the parts and their names, and practise the front view in section and the side or top view. Understand why the taper, clearances and enlarged ends are provided. Questions often ask about the function of the gib or of the taper.