Interesting history

Before the first world war,the need for interchangeability of product components was felt. To ensure interchangeability limit gauges – plain and threaded were required to be developed. The first thread was developed accidentally by Sir Joseph Whitworth. As the story goes, he was filing a log of wood, when his hand slipped resulting in the creation of an angular groove in the wood.

This set him thinking and he invented first thread form (55°), which was named as Whitworth thread. He was the pioneer who standardized screw threads, which are named after him.

Components using various types of threads have been developed, for various end uses. Presently Metric (60°), Unified (60°), Whitworth (55°), BA (47.5°), BS cycle (60°) , ACME (29°), trapezoidal(30°), Standard Buttress (7°/ 45°), NPT/NPTF (60°), BSP, BSPT (55°) are popularly used. Accordingly, gauges to check these thread types have been developed.

Important aspects of gauges are:

  • 1. Raw material: Good quality tool steel with tungsten alloying is generally used. The components are through-hardened and tempered to achieve RC 58 to 61 hardness. SIZECONTROL ensures perfect heat treatment and sub-zero treatment using a dedicated facility.
  • 2. Gauge Blanks: We manufacture gauge blanks as per IS 9631, IS 9608, IS 10685, IS 5388 (for plugs) and IS 9610 (for rings) & aluminium hexagonal blackodized handles to IS
  • 3. Classes of fit: Normally there are three classes of fit depending on the application, viz. close fit, medium fit and free fit. Class groups in various standards are given below:
    Thread type Close fit Medium fit Free fit
    Metric Class 4,5 Class 6 Class 7,8
    Unified Class 3 Class 2 Class 1
    Whitworth Close Medium Free/normal
  • 4. Thread specifications and gauging practice: A number of Indian and international specifications are used for thread specifications and gauging practice. These have been mentioned in the products section against each product group.
  • 5. Coated versus uncoated threads: When threaded components are coated, it is necessary to check the thread before coating and after coating. Gauges for such applications are suitably designed. Normally only the Go limit gauge that needs to be used for checking before coating. Components near the NoGo limit automatically fall within the tolerance limit after coating. Normally the coating thickness is 0.001” Thus the coating gauges are manufactured undersized or oversized depending on the coating thickness. Please consult us for gauges for coated thread components.

Maintenance & Preservation of Gauges

Gauges are precision equipment for checking components and must be used with great care.

  • Gauges need to be thoroughly cleaned before and after use with either petrol or any suitable no-aqueous solvent.
  • Gauges should be stored after coating with Petroleum jelly or suitable mineral oil when not in use.
  • The component to be checked must also be clean and free of metal burr.
  • Do not use the thread gauge forcefully. It is not a tap or die.
  • Do not allow the gauge to be dropped on the shop floor; these gauges are brittle and may break.

Gauge Life

It is very difficult to predict gauge life. Gauges used against cast iron, aluminium have faster wear due to lapping effect. Stainless/duplex have a galling effect . Gauge life can certainly be improved by proper use and care of the gauges as defined above. Troubleshoot Gauges.

Gauge calibration and replacement

It is essential to maintain proper record of gauge use, and keep an eye on the wear. As gauges are checking equipment, these must be replaced as soon as the wear limit is reached. Wear check plug gauges should be used to check the wear limit of the ring gauges. As soon as wear check plug (WCP) enters the ring gauge, the rig gauge must be replaced. Similarly, Wear check ring (WCR) gauge should be used to check the wear of thread plug gauges. Normally WCP and WCR are used to check Go-ring and Go-plugs as there is less wear on No-go gauges