CONSTRUCTION OF WEIGHTS OF DIFFERENT CLASS AS PER OIML (INTERNATIONAL ORGANIZATION OF LEGAL METROLOGY)

1. Class E weights

 A.Class E weights from 1 mg to 50 kg:- Class E weights from 1 mg to 50 kg shall be solid and shall have no cavity open to the atmosphere. They shall consist of a single piece of material.
 B.Class E2 weights greater than 50 kg:- Class E2 weights greater than 50 kg may have an adjusting cavity.

• The volume of this cavity shall not exceed 1/1000 of the total volume of the weight.
• The cavity shall be sealable and shall be watertight and airtight (e.g. by means of a joint). A threaded plug with either a screwdriver slot or a handling device such as a knob, a handle, an eye, etc., shall close the adjusting cavity.
• The material of the plug shall be the same as the body of the weight and shall comply with the surface requirements of class E2.
• After initial adjustment, approximately 1/2 the total volume of the adjusting cavity shall be empty.

2. Class F weights:- Class F weights may consist of one or more pieces manufactured from the same material.

 A.Class F weights from 1 g to 50 kg:- Class F weights from 1 g to 50 kg may have an adjusting cavity. The volume of this cavity shall not exceed 1/4 of the total volume of the weight. The cavity shall be closed either by means of a lifting knob or by any other suitable device. After initial adjustment, approximately 1/2 of the total volume of the adjusting cavity shall be empty.
 B.Class F weights greater than 50 kg:- Class F weights greater than 50 kg may also consist of a box assembled from several pieces, closed and welded airtight and watertight.

• The content of the box may consist of a material different from that of the box and shall comply with the requirements for magnetic properties of class F1 and F2.
• The walls of the box shall be sufficiently rigid that deformations due to changes in ambient air pressure, handling, shocks, etc. cannot occur.
• Class F weights greater than 50 kg may have an adjusting cavity. The volume of this cavity shall not exceed 1/20 of the total volume of the weight.
• The adjusting cavity shall be sealable and shall be watertight and airtight (e.g. by means of a joint).
• A threaded plug with either a screwdriver slot or a handling device such as a knob, a handle, an eye, etc., shall close the cavity.
• After initial adjustment, approximately 1/2 of the total volume of the adjusting cavity shall be empty.

3. Class M weights

 A.Class M1, M2 and M3 weights from 1 g to 50 kg:- Class M1, M2 and M3 weights from 1 g to 10 g shall be solid, without an adjusting cavity.

• For class M1, M2 and M3 weights from 20 g to 50 g an adjusting cavity is optional. Class M1, M2 and M3 weights from 100 g to 50 kg shall have an adjusting cavity. However, the adjusting cavity is optional for class M1 and M2 weights from 20 g to 200 g that are made of stainless steel.
• The adjusting cavity shall be designed to prevent the accumulation of foreign matter or debris, to permit a secure cavity closure and to allow the cavity to be opened for additional adjustments. The volume of the adjusting cavity shall not be greater than 1/4 of the total volume of the weight.
• After initial adjustment, approximately 1/2 of the total volume of the adjusting cavity shall be empty.
• Class M1, M2 and M3 weights from 100 g to 50 kg of the cylindrical type shall have an adjusting cavity coaxial with the vertical axis of the weight, opening on the upper face of the knob and including a widening of the diameter at the entrance. The cavity shall be closed either by a threaded plug with a screwdriver slot or by a disc with a central handling hole. The plug or disc shall be made of brass or of another appropriate metallic material and shall be sealed by a lead plug or similar material driven into an internal circular groove provided in the widened portion of the diameter.
• Class M1, M2 and M3 weights from 5 kg to 50 kg with the rectangular parallelepiped shape shall have an adjusting cavity either formed by the inside of the tubular handle, or, if the handle is solid, an adjusting cavity shall be cast within one of the uprights of the weight, opening on the side or the top face of the weight.
• If the adjusting cavity is in the tubular handle, the cavity shall be closed either by a threaded plug with a screwdriver slot or by a disc with a central handling hole. The plug or disc shall be made of brass or another appropriate metallic material and shall be sealed by a lead plug (or similar material) driven into an internal circular groove or into the threads of the tube.
• If the adjusting cavity is cast within the upright and opens on the side or the top face of the upright, the cavity shall be closed by a plate made of soft steel or of another appropriate material, sealed by a lead plug or similar material driven into a housing having a conical section.

B.Class M weights greater than or equal to 50 kg:- The weights shall not have any cavities that may cause rapid accumulation of dust or debris.

• The weights shall include one or more adjusting cavities. The total volume of all adjusting cavities shall not be greater than 1/10 of the total volume of the weight. The cavities shall be sealable and shall be watertight and airtight (e.g. by means of a joint). The cavities shall be sealable using a threaded plug with either a screwdriver slot or a handling device (e.g. a knob or handle).
• After initial adjustment, at least 1/3 of the total volume of the adjusting cavity shall be empty.