Rounded Bolt Head vs Stripped Screw Drive: How to Tell the Difference

With a rounded head, the outside of the head is worn so a wrench or socket slips. With a stripped drive, the recess in the head is worn so a bit or key slips, while the outer head can still be intact.

They are different conditions, and which one you have changes which categories of approach apply. This guide does not give step-by-step removal instructions.

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Rounded external head

The corners or flats on the outside of a bolt or nut head are worn, so a wrench or socket slips instead of turning it. Some manufacturers describe tools that grip the outside of a worn head, such as extractor sockets; Irwin, for example, describes a bolt extractor for rusted, painted-on, and stripped-out bolts. These need enough of the head's outside surface left and room for the tool to fit around it. Pushing harder can round the head further.

A socket on a ratchet held above a corroded hex-head bolt whose corners are visibly rounded and chipped. — A worn external hex head with rounded, chipped corners. In this image the socket sits above the head rather than on it.

Stripped screw drive

The recess in the head (Phillips, Torx, hex, and similar) is worn, so a bit or key slips or spins in it while the outer head looks fine. What applies depends on what the bit does:

If the bit still partly seats, people try ways of improving the grip between the bit and the recess. This can make the recess worse.
If the recess gives no bite and the head stands above the surface, some people use locking-type pliers on the head's edge.
If the recess gives no bite and the head is flush or countersunk, a screw extractor used in a hole drilled into the head is one category of approach. Drilling too far down can cause the head to pop off, and extractors are made of hardened steel and can break.

Two screw heads side by side with close-ups below: on the left a Torx-style recess with torn, rounded edges, and on the right a recess with sharply defined lobes. — A stripped and an undamaged internal drive. The outer heads look alike; the difference is in the recess. Text inside the image is descriptive only.

How to tell the difference

A wrench or socket slips on the outside of the head: the head is rounded.
A screwdriver, bit, or key slips or spins inside the recess: the drive is stripped.
Look at the head with a light: are the outside corners worn, or the edges of the recess?
If the head is mostly gone and only the shank remains, it is a broken fastener; see Broken Bolt: Protruding, Flush, or Recessed.

Stuck is not the same as damaged

A fastener can be stuck without any damage to its head or drive, and a damaged head or drive can be on a fastener that would turn easily. Corrosion can contribute to a fastener seizing, but visible rust alone does not show whether it will turn.

Applying penetrating lubricant before using force is commonly tried first on a stuck fastener; results vary and nothing is guaranteed. Forcing a stuck fastener can round its head, strip its recess, or break it.

A heavily rusted hex-head bolt and washer on a steel plate, with corrosion spread across the plate around them. — Corrosion around a fastener. Visible rust alone does not show whether it will turn.

When it becomes a broken-fastener problem

If the head shears off or only the shank remains, the condition has changed. See Broken Bolt: Protruding, Flush, or Recessed and the extractor types reference.

FAQ

Why does my wrench slip?

A wrench or socket slips when the outside of the head is worn or rounded, or when the tool does not fit the head properly. If the slipping happens inside the recess instead (a screwdriver, bit, or key), the drive is stripped.

Is a stripped drive recoverable?

It depends on the condition. If the bit still seats, people try ways of improving the grip, which can also make the recess worse. If the recess gives no bite at all, other categories apply, described above. Nothing here guarantees a result.

Does rust mean it is seized?

No. Corrosion can contribute to a fastener seizing, but visible rust alone does not show whether it will turn. Applying penetrating lubricant before using force is commonly tried first on a stuck fastener; results vary.