TOLERANCES OF SCREWS AND GAUGES

The tolerances in screw threads, controlled the standard of UN for ensuring the correct class of fit in screw threads.

Reasons for tolerance:-

Making sure the screws' major, pitch and minor diameter are all in the enveloped boundaries.
Truncation: use of larger tap drill for female threads. (in other words, reduce the diameter of male thread)

Thread are measured using thread gauges. There are two types of gauges:-

-ensuring that the screw DO NOT be in the specified standards.

-GO SCREW PLUG: checking major diameter of the female.

-GO PLAIN PLUG: checking the female's minor diameter.

2. NO-GO GAUGE

-ensuring the screw is in the specified standards.

-checking pitch diameter of low addendum and high addendum

- LOW ADDENDUM: in contact with the thread over short flank length. (better method to check pitch)

- HIGH ADDENDUM: covers larger area of flank length

*NOT-GO GAUGE MUST BE OF ONLY 2 OR 3 TURNS OF THREAD to minimise the error.

GAUGE TOLERANCY

- manufacturing go, no-go gauge.

(*The gauges are not workable naturally for all screw tolerances. so they need to be manufactured.)

-go gauge: placed within the limit and are always assembled.

-no-go gauge: placed outside the limit but unlikely accept small tolerance.

Three gauge tolerances are:-

-ensuring the gauge to continuous use after wear.

-ring and calipers are manufactured this way.

2. Check Gauge

-GO & NO-GO check gauges: verify the size of new solid type ring

-can altered to direct measurement

- necessary for sizes below 1/4 inch diameter

3. Marking Gauge

- each gauge must be marked to show the limit size

TOLERANCES: About