BS 958:1968

This standard BS 958:1968 Specification for spirit levels for use in precision engineering is classified in these ICS categories:

• 17.040.30 Measuring instruments

1.1 This British Standard specifies requirements for spirit levels for use in precision engineering. It provides for three types of levels as follows:

Type 1. A spirit level with an unrelieved flat base of steel hardened and lapped.

This type of level is usually made with base lengths from about 100 mm to 200 mm. The advantage of the lapped base is that the base length of the level can be varied at will by wringing two slip gauges on to the base at the desired distance apart.

Type 2. A spirit level, mounted in a body usually of cast iron or steel, having a base formed with flat bearing surfaces at the two ends, i.e. the middle portion is relieved.

The bearing surfaces may either be plain or contain a longitudinal 120° V-groove for use on cylindrical surfaces. In the latter case a short cross-level or small circular level is provided.

This type of level is usually made with base lengths from about 250 mm to 500 mm.

Type 3. A square block level, usually of cast iron, and about 200 mm square.

Accuracy of performance for three types of level. Sensitivities and scale, general features of design, adjustments and finish, accuracy of working surfaces. Notes on the choice of sensitivity of a level appended.