No. of groups segregated in selective assembly depends upon desired tolerance and process capability of machine. Conditions like high quality and low cost can be achieved by selective assembly technique.

Use of double ended gauges is unnecessary in this case because diameter difference between low and high limit of tolerances is converted into lengthwise dimension. Thus hole will be within tolerance. Diameter at large end of hole falls between gauge plane and or line at distance Z from it.

?Go? limit is applied to limit corresponds to maximum material limit condition that is lower limit of hole and upper limit of shaft while ?No Go? limit is applied to minimum material condition that is upper limit of a hole and lower limit of a shaft.

Loose tolerance results in increase in cost, assembly problems and poor performance of product. Tight tolerance results in unnecessary machining and inspection time.

3 lines are drawn with Persian blue along length on plug gauge or spindle to test taper. It is fitted in gauge and rotated once or twice. If se marks of Persian blue are not rubbed evenly n taper is not correct.

?Go limit? deals with upper limit of shaft and lower limit of hole and refers to maximum material condition. ?No-go? limits deals with lower limit of shaft and upper limit of hole and refers to minimum material condition.

Shaft ?h? gives clearance fit and available in grades 5 to 11. It is useful for spigot fits. Shaft ?k? is a transition fit and it is best suited for location fits. Grades available for this category are also 5 to 11.

Good quality steel is used for making se gauges and se are suitably heat treated to give hardness of 750 to 860 HV and for stabilization. Gauges surfaces should be free from rust, crack and burrs.

Upper deviation is positive when maximum limit of size > its basic size and negative when maximum limits size < basic size. For lowers deviations, it is a positive quantity when minimum limit size is more than its corresponding basic size.

Fixed gauges are generally error free due to drift of original adjustment, effect of variation of power, non-linear response etc. Human errors are almost nil except for careful handling. Auxiliary equipment and setups are not required.