Short answer
A nail is driven into wood and may have a smooth or textured shank; a wood screw has a head, shank, thread, and core, with its threaded portion engaging the wood. Threads alone do not separate them: the USDA handbook also identifies annularly and helically threaded nails. The fastener’s construction and documented type matter more than one visible ridge. 1 2
On this page
At a glance
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| Attribute | Nail | Screw |
|---|---|---|
| Shank features | Smooth, threaded, or barbed forms | Thread and core identified as principal parts |
| Head shapes | Include flat, oval, countersunk, and brad | Common wood screws: flat, oval, round |
| Installation evidence here | Explicitly described as driven | Installation mechanism not explained |
| Are threads decisive? | No: threaded nails exist | Threads are part of screw anatomy |
These descriptions concern wood fasteners, not every specialized fastener. 1 2
What each thing is
“Nail” names a family, not just the familiar smooth wire form. The handbook includes coatings, barbs, and multiple threaded forms within that family. Its wood-screw discussion instead organizes the fastener around head, shank, thread, and core. These are category descriptions, not mutually exclusive silhouette tests. 1
Key differences
Nails are typically driven, and their shank, surface treatment, and penetration affect how they resist withdrawal and lateral loads. Wood screws have a defined threaded portion; the handbook relates screw withdrawal to thread penetration, screw diameter, and wood properties. These are different fastening constructions, but neither name alone promises a higher load capacity. 1 2
How to tell them apart
Check the fastener’s designated type and construction. A screw has a threaded core and shank; a nail may be smooth or have annular or helical ridges. Thus visible threads do not rule out a nail. A product specification is more reliable than judging a partly hidden fastener by its head or exposed shank. 2
Where they overlap
Head shape is another shared feature. Both nail and wood-screw classifications include flat and oval heads, so those outlines cannot settle identification. Nails also include countersunk forms, while flathead wood screws are associated with a flush surface. Appearance at the wood surface is therefore not a sufficient boundary. 1 2
Edge cases
A helically threaded nail is the useful boundary case: its spiral-looking shank does not change the handbook’s classification of it as a nail. Annularly threaded nails likewise remain nails. The distinction must preserve these named subtypes rather than redefine every threaded fastener as a screw. 1
Why the distinction exists
Separate names retain information that broad resemblance loses. The handbook discusses nail driving, shank modifications, and withdrawal behavior within its nail treatment, then gives wood screws their own anatomical description. Keeping those categories separate allows a textured nail to remain distinguishable from a wood screw without denying their shared features. 1
Common misconceptions
Neither “all nails are smooth” nor “a flat head means screw” fits the handbook’s descriptions. Nor does either category automatically make a stronger joint: withdrawal and lateral resistance depend on the wood, fastener dimensions, and conditions of use. 2
Examples
Two hypothetical identifications apply the source descriptions. First, a package labeled annularly threaded nails contains ridged fasteners: the ridges are consistent with a nail subtype, not evidence of mislabeling. Second, a flathead wood screw intended for a flush surface remains a screw; its head shape alone would not distinguish it from every nail. 1