Granite Parallels

UKAS Certified | Hand Lapped | BS 906:1972

Hand‑lapped to BS 906:1972 Eley’s granite parallels deliver exceptional stability and precision for accurate height gauging and parallelism checks. Each pair features two highly parallel master faces for repeatable referencing in rigorous metrology applications. 

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  • Available in laboratory (Grade A) and inspection (Grade B) grades.

  • Two highly parallel master faces: hand‑lapped to tight tolerances for consistent, repeatable referencing.

  • Geometry that provides stable support: for components, gauges and fixtures to maintain precise alignment and height relationships during inspection and setup.

  • Highly accurate reference planes and spacing: improve the reliability of height gauge and dial indicator readings when used with granite surface plates.
  • Height gauging and component fixturing.
  • Parallelism checks and creation of reference steps above a surface plate.
  • Support for height gauges, dial indicators and comparative measurement techniques.
  • Helping to check parallel faces on machined. components

Granite Parallels to BS 906 (1972) Standard Sizes & Overall Flatness

GRADE
SIZE (mm)
SQUARENESS (µm)
PARALLELISM (µm)
A
200 x 40 x 20
5
6
A
250 x 50 x 25
10
10
A
300 x 60 x 30
10
10
A
400 x 100 x 50
15
12
B
200 x 40 x 20
10
12
B
250 x 50 x 25
20
20
B
300 x 60 x 30
20
20
B
400 x 100 x 50
30
25

Related Measurement Solutions

Digital Height Gauges

Use digital height gauges with parallels for repeatable comparative measurements on multiple components.

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Granite Surface Plates

Set granite parallels on our granite surface plates to support parts at controlled heights for inspection and layout.

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Industries Used In - Granite Parallels -

Side view of a factory worker in blue uniform and safety gear setting up raw material on a metal milling machine.

Machine Tool Manufacturing

Setting up work on machine tables, checking parallelism of tables, fixtures and test pieces, and supporting components during machine geometry checks.


Machine tool manufacturers use granite parallels together with surface plates and straight edges to verify parallelism between mounting surfaces and guideways on CNC and conventional machines.

A female aerospace technician in blue overalls inspecting a complex aircraft jet engine component.

Aerospace & Aviation

Raising and supporting structural components, precision brackets, and complex machined parts during layout, CMM, and surface plate inspection while maintaining parallelism.


Aerospace manufacturers use granite parallels wherever tight tolerances, rigid support, and low thermal expansion are required for reliable dimensional verification of critical components.

Unfinished car bodies moving along an automated assembly line track inside an automotive manufacturing facility.

Automotive Manufacturing

Supporting engine blocks, gearbox housings, and precision components at controlled heights for CMM inspection, surface plate checks, and machining operations.


Automotive manufacturers rely on granite parallels to maintain consistent part positioning and to verify parallel faces on safety‑critical and high‑performance components.

Close-up of a high-power CNC laser cutter head piercing a reflective metal sheet, producing bright golden sparks.

Precision Engineering

Supporting parallelism checks on precision components, verifying equal heights, and ensuring accurate spacing between parts and fixtures on surface plates and machine tables.

 

Precision engineering companies use granite parallels as stable reference standards for parallel faces and consistent set‑ups in grinding, milling, and inspection operations.

Close-up of an inspector in a blue uniform using a handheld digital vernier calliper to measure a cylindrical metal shaft.

Metrology & Calibration Labs

Providing a reference for parallelism measurement, height comparison, and part support on granite surface plates during dimensional inspection and calibration work.


Metrology and calibration labs use granite parallels to create reliable inspection datums, raise parts with complex features, and ensure repeatable, traceable geometric measurements.

FAQs

What is the difference between 2-face and 4-face granite parallels?

A 2-face parallel has two narrow opposite faces precision lapped flat and parallel, providing a matched-height reference on the top and bottom surfaces.

 

A 4-face parallel has all four longitudinal faces lapped flat and parallel, offering greater versatility; any face can be used as a reference surface, and the parallel can be rotated to present a different height or face depending on the inspection setup. 4-face parallels are the preferred choice for high-precision laboratory and inspection environments where maximum flexibility is required.

 

Both configurations are supplied in matched pairs to ensure consistent height across the pair.

Calibration frequency should reflect usage intensity, application criticality and your QMS requirements. As a practical guide, parallels in high-cycle production or shop-floor environments benefit from calibration every 6–12 months; those in controlled laboratory settings may suit an annual interval. In regulated sectors such as aerospace or medical device manufacturing, more frequent calibration is commonly specified to prevent measurement drift from impacting product decisions.

 

Calibration should also be triggered following any impact, suspected damage or anomalous measurement results. All Eley granite parallels can be supplied with UKAS traceable calibration and we offer ongoing recalibration to BS 906:1972.

 

For any calibration requirements, contact our team today.
Email: sales@eleymet.com
Phone: 01332 367475

Grade A (Laboratory Grade) is manufactured to tighter parallelism tolerances per BS 906:1972 and is the correct choice for UKAS-accredited laboratories, primary reference applications and high-precision inspection environments where measurement uncertainty must be minimised. Grade B (Inspection Grade) suits quality department inspection and production-environment setups where the tighter Grade A tolerances are not critical.

 

As with all reference standards, a clear traceability hierarchy should be maintained – with a Grade A pair used to periodically verify any Grade b working parallels.

Size selection is driven by the height clearance required beneath the workpiece and the length of the component being supported.

 

Eley granite parallels are available in a range of standard lengths, widths and thicknesses, from compact sizes suitable for small component inspection through to larger parallels for supporting long or heavy workpieces on surface plates and CMM tables. As a practical guide, the parallel height should provide sufficient clearance for the measuring instrument to access all required datum features without repositioning, and the length should fully support the workpiece to prevent rocking or tipping.

 

Bespoke sizes and configurations are available where standard offerings do not meet specific application requirements.

Contact our team today to discuss your unique requirements.
Email: sales@eleymet.com
Phone: 01332 367475

Granite parallels offer several practical advantages over their steel equivalents. They are non-magnetic, critical when inspecting components that must not be exposed to magnetic fields, or when using sensitive electronic gauging equipment. They are rust-free, eliminating the need for rust-prevention treatments and the risk of corrosion-related surface damage in coolant-rich environments.

 

Granite also has a lower coefficient of thermal expansion than steel, providing greater dimensional stability across temperature fluctuations common on the shop floor. When surface damage does occur, granite chips rather than raising a burr, making degradation visible and less likely to go undetected and corrupt measurements.

Granite parallels require straightforward but consistent care:

  • Cleaning: Wipe all working faces before and after use with a lint-free cloth and a specialist stone cleaner or denatured alcohol. Never use water-based or aggressive solvents.
  • Handling: Always handle parallels carefully to avoid edge impacts. Set them down gently on clean, flat surfaces.
  • Storage: Store in matched pairs, covered and protected from dust and particulate contamination, in a stable, temperature-controlled environment.
  • Inspection: Regularly check working faces for chips or contamination. Any suspected deviation from parallelism tolerance should be referred for professional recalibration.
  • During use: Ensure the surface plate is clean before placing parallels, and confirm there is no debris between the parallel and the surface that could affect the height reference.

Eley offers resurfacing and recalibration to restore granite parallels back to BS 906:1972 specification.

Yes. Granite parallels are supplied as matched pairs to ensure both parallels within the set are at a consistent, verified height — a critical requirement when supporting a workpiece across two points. The height difference within a matched pair is held to tight tolerances in accordance with BS 906:1972, ensuring that any workpiece resting across the pair sits on a true, stable reference plane without rocking.

Yes. All Eley granite parallels can be supplied with a UKAS traceable calibration certificate from our UKAS-accredited laboratory (No. 30213). The certificate documents the measured parallelism deviation, height matching tolerance and measurement uncertainty, providing the documented evidence required for QMS frameworks.

Yes. Granite parallels that have moved out of tolerance can be professionally resurfaced and recalibrated rather than replaced.

 

Eley’s engineers hand-lap the working faces back to BS 906:1972 specification, followed by UKAS traceable re-verification. This extends the working life of the parallels and is a cost-effective alternative to replacement, particularly for larger or matched-pair sets. Work can be carried out at our Derby laboratory or on-site where appropriate.