What is the difference between a sleeve and cotter joint and a gib and cotter joint?

A sleeve and cotter joint joins two round rods using a sleeve and two cotters. A gib and cotter joint joins a square rod end to a strap using one cotter and a gib that stops the strap opening.

What is the taper of a cotter?

Usually 1 in 30 (sometimes up to 1 in 24). It is on one side only and makes the cotter self-locking.

Where are cotter joints used?

Where two rods carry axial pull or push and must be separable: piston rod and crosshead, pump rods, strap ends of connecting rods, and foundation bolts.

Rod Joints: Sleeve & Cotter and Gib & Cotter Joint

A cotter joint joins two rods end to end so that they can carry a pull or a push along their length, and can still be taken apart. A cotter is a flat steel wedge with a small slope (taper) of about 1 in 30. In a sleeve and cotter joint, a hollow sleeve covers both rod ends and two cotters lock them. In a gib and cotter joint, a strap wraps around the square end of one rod and a gib plus a cotter lock it. In drawing, every size is written as a multiple of the rod diameter d.

What is a cotter joint?

A joint connects two parts. A cotter joint connects two rods that are in a straight line (coaxial) and carry an axial load: a pull (tension) or a push (compression) along the rod. It is a temporary (detachable) joint: you can knock out the cotter and separate the rods. It is not used for a rod that turns (rotates), because the cotter could loosen.

A cotter is a flat bar of steel, thick in one direction and thin in the other. One side is slanted. This slope is called the taper, usually 1 in 30 (it can be up to 1 in 24). A small taper means the cotter stays in by friction: it is self-locking. The ends of the cotter are rounded.

Sleeve and cotter joint

Used to join two round rods of the same size.

Parts: two rods (each with an enlarged end), one sleeve (a hollow cylinder) and two cotters.
Rectangular slots are cut through the sleeve and through each rod end. The slots are a little longer than the cotter is wide, which leaves small gaps called clearances (about 3 mm).
When the cotter is driven in, its taper pulls each rod towards the centre. The rod ends then press on each other (or nearly), and the joint becomes tight.

Typical proportions (d = rod diameter)

Enlarged rod end ≈ 1.2d; sleeve outside diameter ≈ 2.5d; sleeve length ≈ 4d; cotter thickness ≈ 0.3d; cotter width ≈ 1.2d; taper 1 in 30. Different books use slightly different numbers; always follow the sizes given in the question.

Gib and cotter joint

Used for rods with a square or rectangular end, for example the strap end of a connecting rod.

Parts: one rod with a square end, a U-shaped strap that wraps around it, a gib and a cotter.
The gib is a steel piece with a straight face and two hooked ends (heads). It sits beside the cotter.
Why a gib? When the cotter is driven, friction would bend the two arms of the strap outward (open it). The hooked gib holds the arms together. The gib also gives the cotter a wide flat face to slide on, so wear is less.
The taper is on the cotter side only; the gib's two faces are parallel. Gib and cotter together form a rectangle with parallel outer faces.

Some designs use two gibs; a set screw or a split pin can stop the cotter from slipping out.

How to draw rod joints (exam tips)

Questions usually ask for a front view (upper half in section) and a side view, or an assembly from given parts.

Draw the centre line first. Mark all sizes from the rod diameter d.
Draw the rods, then the sleeve or strap, then the slots, then the cotter last.
Show the taper of the cotter clearly (it is small, so draw it slightly exaggerated if asked).
Show clearances as small gaps. Do not hatch rods, cotters or gibs that are cut along their length; hatch the sleeve or strap.
Write the title, scale and part list (rod, sleeve, cotter, gib, strap).

Key formulas and definitions

Taper of cotter = (wide end − narrow end) ÷ length ≈ 1/30
Sleeve outside diameter ≈ 2.5d · sleeve length ≈ 4d
Cotter thickness ≈ 0.3d · cotter width ≈ 1.2d
Axial load on joint = stress × area (pull or push only)

Worked examples

1. A cotter is 150 mm long. Its wide end is 40 mm and its narrow end is 35 mm. Find the taper.

Taper = (40 − 35) ÷ 150 = 5 ÷ 150 = 1/30. So the taper is 1 in 30.

2. For a sleeve and cotter joint with rod diameter d = 30 mm, find the sleeve outside diameter, sleeve length and cotter thickness using 2.5d, 4d and 0.3d.

Sleeve outside diameter = 2.5 × 30 = 75 mm. Sleeve length = 4 × 30 = 120 mm. Cotter thickness = 0.3 × 30 = 9 mm.

3. A rod with a square end must be joined to a strap. Which joint do you choose and why?

A gib and cotter joint. The square end fits inside a strap, and the gib stops the strap arms from opening when the cotter is driven, while giving the cotter a flat sliding face.

4. A cotter with taper 1 in 30 is driven 15 mm further. By how much does it pull the rod?

Sideways movement = 15 × (1/30) = 0.5 mm. The rod is pulled about 0.5 mm. A small taper gives a strong but small pull and stays locked.

Common mistakes

Drawing the cotter with parallel sides: a cotter always has a taper on one side (about 1 in 30).
Forgetting the clearances in the slots: without gaps, the cotter cannot pull the rods together.
Using a cotter joint for a rotating shaft: cotter joints are for axial pull or push, not for turning shafts.
Hatching the cotter, gib or rod in a sectional view: solid parts cut along their length are not hatched; hatch the sleeve or strap.

Practice quiz

Practice: answer these yourself

Type or choose your answer, then press Check. Use a hint if you are stuck; the full solution appears after you answer.

Rod Joints: Sleeve and Cotter, Gib and Cotter

🎬 Step-by-step story

🤔 Common doubts, cleared

Why not just weld the two rods?

Why are the rod ends made thicker?

How does a wedge pull the rods together?

Why leave gaps in the slots?

What does the gib do?

What happens if the cotter is only half driven?