Taps - Plug - UNC

Taps are tools used by engineers for creating a female thread inside a hole. The tap is inserted into a special wrench and turned whilst cutting oil is used to lubricate the tap.

When forming a brand new thread in a blind hole, it is usually a three-stage process.

UNC stands for Unified National Coarse. It is a common imperial thread type with less threads per axial distance than its UNF equivalent.

Unified thread types (UNF and UNC) were introduced at the beginning of World War 2 to enable the interchangeability of machinery manufacturing between the USA, Canada and Great Britain. Still commonly found on a vast array of old machines and vehicles in the UK, UNF and UNC threads continue to be the standard thread in the USA and Canada.

Using taps

  • Firstly a taper tap is used. This tap has a pronounced taper to the cutting edges, ensuring that the first cut is less aggressive.
  • After the taper tap comes a second tap. This also has a tapered edge, but not as pronounced as the taper tap. This slight taper helps align the tap when it is first introduced to the hole.
  • The third and final stage is carried out with a bottoming tap, often referred to as plug tap. Bottoming taps have hardly any taper and a continuous cutting edge.

When cutting shallow female threads, it may be possible to skip the third stage and just use the taper or second taps.

If tapping into a soft material it is possible to cut the thread with only a second tap.

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No12 UNC - Plug Tap Presto 60100
£23.78 £28.54
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