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Description
GRADE2 per DIN 875
PERPENDICULARITY0.060 mm
ARMS400 × 250 mm
CROSS SECTION45 × 9 mm
Try square with base 400x250 – DIN 875 right-angle reference
KINEX technical data, grade 2
| Technical data | |
|---|---|
| Standard | DIN 875, form B |
| Accuracy grade | 2 (DIN 875/2) |
| Long arm H | 400 mm |
| Short arm L | 250 mm |
| Arm cross section a × t | 45 × 9 mm |
| Base height c | 9 mm |
| Perpendicularity tolerance | 0.060 mm |
For checking squareness and marking out 90° lines, use try square with base 400x250 KINEX. The arms have a 45 × 9 mm cross section, and the base beneath the short arm is 9 mm high, allowing the instrument to stand unsupported. Grade 2 according to DIN 875 limits perpendicularity deviation to 0.060 mm over the 400 mm arm.
The 400 mm arm checks tall workpiece walls in a single placement, while the short 250 mm arm provides a long reference for marking out.
Workshop try square with base in practice
Four tasks, one precision instrument
TASK 01
Checking perpendicularity against the light
Stand the square on its base on a surface plate and move the 400 mm arm against the workpiece face without applying pressure. Position a lamp behind the contact and view the contact line from the front.
✓ Result: no light gap over the full height indicates a deviation below the method's visibility threshold. A wedge of light at the top or bottom shows the direction in which the face deviates from 90°.
TASK 02
Measuring the gap with a feeler gauge
Insert the blades into the widest part of the gap, starting with the thinnest. The thickest blade that enters without pressure indicates the gap size.
✓ Result: a result in hundredths of a millimeter – starting at 0.03 mm, the thickness of the thinnest blades in the sets.
TASK 03
Scribing a perpendicular line with a layout square
The base projects below the plane of the arm. Lay the square flat, press the base against the reference edge, and guide the scriber along the arm.
✓ Result: a line at 90° to the edge, repeatable with each placement. This is how a layout square with a base works.
TASK 04
Workpiece corner and shoulder
Place the internal angle around the external corner of the workpiece. Use the external angle to check a shoulder: the base rests on the bottom, and the arm contacts the face.
✓ Result: DIN 875 applies the perpendicularity tolerance to both the internal and external angles. The corner relief prevents the workpiece edge from bearing against the square.
Grade 2 precision try square with base – what 0.060 mm means
Tolerance zone, calculation, and grade selection
Perpendicularity tolerance is a zone, not a "plus or minus" deviation. Its width for grade 2 is given by the DIN 875 formula.
t = 20 + 400 / 10 = 60 µm = 0.060 mm
t – perpendicularity tolerance for grade 2 per DIN 875: 20 µm plus one tenth of the arm length in millimeters (1 µm = 0.001 mm). In angular terms, this is approximately 31″, less than one angular minute (″ – angular second, 60″ = 1 minute). At a height of 400 mm, the arm may deviate from perfect vertical by no more than 0.06 mm.
Perpendicularity tolerance of the 400x250 square per DIN 875
| Arm length | Grade 0 | Grade 1 | Grade 2 |
|---|---|---|---|
| 75 mm | 0.007 mm | 0.014 mm | 0.028 mm |
| 100 mm | 0.007 mm | 0.015 mm | 0.030 mm |
| 150 mm | 0.008 mm | 0.018 mm | 0.035 mm |
| 200 mm | 0.009 mm | 0.020 mm | 0.040 mm |
| 250 mm | 0.010 mm | 0.023 mm | 0.045 mm |
| 300 mm | 0.011 mm | 0.025 mm | 0.050 mm |
| 400 mm* | 0.013 mm | 0.030 mm | 0.060 mm This product |
| 500 mm | 0.015 mm | 0.035 mm | 0.070 mm |
| 600 mm* | 0.017 mm | 0.040 mm | 0.080 mm |
| 750 mm | 0.020 mm | 0.048 mm | 0.095 mm |
| 1000 mm | 0.025 mm | 0.060 mm | 0.120 mm |
Note: perpendicularity tolerance is the zone width referenced to the underside of the base, not a "±" deviation. Values apply at 20 °C. Grade 00 applies only to knife-edge squares. * Length not listed in the DIN 875:1981 table – value calculated using the standard's formula.
Arm flatness tolerance per DIN 875
| Arm length | Grade 0 | Grade 1 | Grade 2 |
|---|---|---|---|
| 75 mm | 0.003 mm | 0.006 mm | 0.011 mm |
| 100 mm | 0.003 mm | 0.006 mm | 0.012 mm |
| 150 mm | 0.004 mm | 0.007 mm | 0.014 mm |
| 200 mm | 0.004 mm | 0.008 mm | 0.016 mm |
| 250 mm | 0.005 mm | 0.009 mm | 0.018 mm arm L |
| 300 mm | 0.005 mm | 0.010 mm | 0.020 mm |
| 400 mm* | 0.006 mm | 0.012 mm | 0.024 mm arm H |
| 500 mm | 0.007 mm | 0.014 mm | 0.028 mm |
| 600 mm* | 0.008 mm | 0.016 mm | 0.032 mm |
| 750 mm | 0.010 mm | 0.019 mm | 0.038 mm |
| 1000 mm | 0.012 mm | 0.024 mm | 0.048 mm |
Note: flatness and straightness apply to each arm separately – the green rows represent arm H and arm L of this square. Side faces of the arms: 6 × the tabulated value. Values apply at 20 °C. * Length not listed in the DIN 875:1981 table – value calculated using the standard's formula.
The workpiece tolerance should be at least 4 times, and preferably 10 times, the instrument tolerance. For 0.060 mm, this gives 0.24 mm (1:4) and 0.6 mm (1:10). The try square with base 400x250 can therefore reliably assess perpendicularity with a tolerance of 0.6 mm or greater, or 0.24 mm or greater under the 1:4 rule.
How to check perpendicularity with a steel try square with base
The light gap method step by step
Inspection with a workshop square in 4 steps
1Clean
the square and workpiece, remove burrs from the edges
2Place
the base on a surface plate or on the workpiece datum surface
3Move
the arm against the face being checked without applying pressure
✓Assess
the gap against the light, and its width with a feeler gauge
The underside of the base is the measurement datum.
▲
Method limitations
Do not tilt the square to contact the workpiece with only the edge of the arm. DIN 875 prohibits using flat squares and try squares with bases this way; a knife-edge square is used for edge-based inspection. The absence of a light gap does not prove that the workpiece is within its tolerance – only that the deviation is below the method's detection threshold.
A base as the datum, two measuring angles, and a tolerance of 0.060 mm – the try square with base 400x250 combines perpendicularity inspection, layout work, and corner checks in one instrument. Workshop squares without an accuracy grade have no specified tolerance. This grade 2 precision square per DIN 875 has a tolerance calculated using the standard's formula. After use, wipe it and store it in its case with a thin film of oil.
Questions about the try square with base
Grade, tolerance, calibration
A flat square (form A according to DIN 875, designation MKSa) is a flat L shape. A try square with base (form B, designation MKSc) has a base wider than the arm beneath its short arm. The base allows the square to stand unsupported on a surface plate and rest against the workpiece edge during marking out.
No. 0.060 mm is the tolerance zone width: the distance between two parallel planes perpendicular to the base. The measuring surface of the arm must lie between them. The "±" notation suggests a deviation of 0.060 mm in each direction, meaning a zone twice as wide.
A grade 2 precision try square with base per DIN 875 is used for layout work, setting up workpieces on machine tools, and checking perpendicularity in production. With a 400 mm arm, it permits a deviation of 0.060 mm, so the square can reliably assess workpiece perpendicularity with tolerances of approximately 0.24 mm or greater – the workpiece tolerance is then at least 4 times the instrument tolerance.
Squares are not subject to legal metrological control in Poland, so legal verification does not apply. Calibration is voluntary, and its frequency is determined by the user, for example within a quality system. After a drop or impact, check perpendicularity before further use.
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