When the hole is larger than the fastener needs, when the material is thin or soft, or when a standard washer is already indenting the surface.

Oversized and slotted holes need a washer that comfortably covers the opening at every position the connection can occupy.

Thin sheet, plastics, composites and boards are prone to pull-through, and a larger bearing area is the direct answer.

Worn or damaged holes can often be recovered by bridging with an oversized washer on both faces.

If a standard washer has embossed itself into the component, the area was too small and the next size up is the fix.

In a designed structural connection the washer is specified, and substituting a larger one is a change to the design.

Because they are usually the same thickness as standard washers, so the extra diameter is unsupported.

Under a torqued bolt the washer behaves like a small circular plate, and a wide thin plate bends at its rim.

Once the rim lifts, it is no longer bearing on anything, and the effective area shrinks back towards that of a standard washer.

The visible symptom is a washer that has cupped and a bright ring where it was still in contact.

Thicker plate washers, or square plate washers in timber work, solve it properly.

Reducing the torque is not a solution, because it reduces the clamping force the joint was meant to have.

It can bridge the damage and restore a usable fixing, but it does not restore the material's strength.

Bearing on sound material either side of the tear works well for light and moderate loads, particularly with washers on both faces.

The torn area itself is carrying nothing, so the connection's capacity is whatever the remaining sound material provides.

In a structural member, a tear is a section loss and needs an engineered repair rather than a washer.

Repeated tearing at the same fixing is a sign the load exceeds what the material can carry, and more washers will not change that.

For sheet and cladding work, an oversized washer with a sealing element is often the correct and durable repair.

In practice very little - the names come from different trades and markets for the same idea.

All three describe a washer with an outside diameter substantially larger than the standard series for that bore.

Actual dimensions vary between suppliers and regions, so the outside diameter should be read from the specification rather than assumed from the name.

Some names imply a particular thickness in particular markets, which is another reason to check the dimension.

Plate washers and structural plate washers are a distinct product, being thicker and often square.

When ordering, quoting bore, outside diameter and thickness removes the ambiguity entirely.

Only where the connection design calls for them - and then usually as a specified hardened or plate washer rather than a stamped oversized one.

Slotted and oversized holes in structural steelwork require washers that cover the opening and resist indentation under high-strength bolts.

Those are specified products with stated thickness and hardness, not general oversized washers.

Using a soft stamped washer under a high-strength bolt loses preload into deformation of the washer.

Timber connections often require large square plate washers, sized in the design for the bearing strength of the timber.

The rule holds throughout: a designed connection names its washer, and naming it is not decoration.

On thin or damaged material, yes - the pull-through problem exists on both faces.

A large washer on one side and a bolt head on the other simply moves the failure to the unprotected face.

In sheet metal repairs, washers both sides is the normal detail.

Where one side is a thick structural member and the other is thin sheet, only the sheet side needs it.

Both washers should be large enough to cover any oversized hole on their own face, since holes are not always the same size through the stack.

Adding washers increases the grip length, so a longer fastener may be needed.

Yes - a larger bearing surface increases friction under the turning face, so more torque produces less clamping force.

Most of the torque applied to a fastener is consumed by friction rather than converted into tension.

A larger friction radius under the head or nut raises that share, so a torque figure developed with a standard washer over-estimates the preload achieved.

The effect is larger with rough or unlubricated surfaces.

Where preload matters, the torque figure should be derived for the actual assembly rather than carried over.

For general fixing this is academic; for a designed joint it is one of the reasons washers are specified rather than chosen on site.