□ Square
Square · Indicadores dimensionales · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “□ 12” states a square requirement.
What controls
A symbol placed before a dimension to indicate that the cross-section of the feature is square with that side length, avoiding repeating the same dimension in two directions. It is a dimensioning convention: it states that both sides are equal and share the same tolerance. What it does not say anything about is the perpendicularity between the faces or the shape of the section: a feature can meet both side dimensions and still be a rhombus. If that relationship matters, a separate geometric tolerance is needed.
How to verify
A micrometer or caliper for the two across-flats dimensions, and a check of the angle between faces with a square, a dial indicator or coordinate measurement. The quickest functional check is to measure the two diagonals: if they differ, the section is not square no matter how equal the sides measure. For features that have to fit into something, a square socket gauge settles the check in one go.
Common mistakes when interpreting it
- Assuming the symbol guarantees that the faces are perpendicular to each other.
- Checking only the two across-flats dimensions and not the diagonals.
- Applying the side tolerance to the diagonal, which varies more than the dimension itself.
How to get it in the workshop / if it comes out of tolerance
Common on shaft ends for wrenches, on studs and on guides. In machining, the square section is produced with four positions of an indexer or by milling with a fourth axis, and the typical error is not size but the angle between opposite faces: the dimensions come out fine and the square comes out as a rhombus. If the part fits into a square socket, the actual fit depends on the diagonal, not the side.
Correct sides but impossible fit: measure the diagonals; the problem is the angle between faces, and it comes from indexer accuracy or fourth-axis repositioning. If one face comes out tapered, check clamping rigidity and overhang. And if the square has to fit with a defined clearance, bear in mind that taking the sides down to gain clearance also makes the diagonal worse.
Related symbols
Other symbols in Dimension indicators
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