GMT uses Indian black granite which is best suited for metrology application
Why GMT Granite Products?
GMT metrology is a manufacturer and supplier of granite surface plates of grade 00, grade 0, grade 1. grade 2 and grade 3.

GMT’s metrology division is located at Hosur, Tamil Nadu. This region is home to large deposits of world famous Indian black diabase granite. Indian black granite is best suited for metrology application as this granite has a very fine-grained structure. The properties, which help in selecting a rock for metrology application are density, water absorption & porosity, flexural and compressive strength.

AS PER IS 7327-2003 / * AS PER DIN 876:84

Surface plates are used as reference planes for dimensional inspection and calibration of mechanical artifacts. This plate acts as a datum line or surface. So, the flatness of the plate is critical. This flatness measurement commonly carries a tolerance and may include a grade designation. GMT Metrology Granite Surface Plates meet the DIN and IS Standards specified in the table above. Granite Surface Plates are manufactured to precision standards using the highest quality granite.

Rigorous quality control inspection is carried out at all stages. Final inspection is carried out with a High Precision Computerised Electronic Level calibrated by an NABL accredited lab at regular intervals.

Accuracy under Load
Granite Surface Plates are capable of supporting a total normal load of 25 kgs. per 0.1

A certificate of accuracy is supplied with each plate as per standards specified.

Technical Data
Granite Surface Plates are manufactured in five grades. The typical application of these five grades of plates is as under :
1. GRADE 00 as per DIN : 876 : 84 is of laboratory grade. It is specified for precision measurement in gauge rooms and metrology laboratories for calibration masters.
2. GRADE 0 is of inspection grade. It is specified for general work in quality control.
3. GRADE 1 is of tool room grade. It is specified for production checking work through the shop.
4. GRADE 2 & 3 are intended for use in shops for general inspection. The choice of Grade 2 & 3 will depend on the application needs of the customer.

Granite Surface Plates are made from select granite with uniform distribution of light and dark constituents. In such granite the minerals are evenly distributed resulting in a homogenous appearance. The following are the representative properties of our granites :
Texture : Fine
Specific Gravity : 3.08 g/cm3
Hardness : Scleroscope over 90
Modules of Elasticity : 9.0 to 12.0 x 105kg/cm2
Moisture of absorption : Nil

The flatness deviation of a local area of 250 mm x 250 mm of the working surface shall not exceed :
1. 3.0 µm for plates of Grade 00
2. 3.5 µm for plates of Grade 0
3. 7.0 µm for plates of Grade 1
4. 15.0 µm for plates of Grade 2
5. 30.0 µm for plates of Grade 3

These are fabricated of heavy angle iron and reinforced to ensure rigidity. The stands are designed to withstand the weight of the granite surface plates and are supplied with 3 leveling screws for leveling the granite surface plates.

Plate will be supplied with a suitable Rexine Cover to protect both the working surface and side faces of the plate at extra cost.