Understanding Key Differences Between NPT and NPTF Taps
Taps are used to cut internal threads in valves, couplings, unions or fittings that will be mated with threaded pipe or fittings to make a pressure tight joint. Selecting taps for cutting taper pipe threads requires some investigation to ensure two important requirements are met. First, to provide the correct mating threads in the assembly and secondly, choosing the right style tap to meet specifications and produce quality threaded parts in the quantity required. The most common American styles are National Pipe Taper (NPT) and National Pipe Taper Fuel (NPTF).
NPT threads are used in mechanical or low-pressure air or fluid applications and the use of sealant or tape is adequate to prevent leakage. NPTF taps are made to different specifications so that in addition to sealing on the flanks of the thread like the NPT form, the threads also seal at the joining of the crest and root of the assembled threads eliminating the possibility of leakage. The use of an NPTF marked tap for NPT applications is appropriate, however NPT taps cannot be used for dryseal (NPTF). When visually comparing these two styles in the same size they look identical. Both have a ¾” taper in 12 inches of length and at the top of a threaded hole the pitch diameters are the same, the variation is in the crest and root specifications of the NPTF tap.
Tapping pipe threads requires higher cutting forces than straight thread tapping, because taper pipe threads require 100% thread depth engagement, while straight UNC or UNF forms normally use 75% thread depth. All threads on tapered pipe taps are cutting when fully engaged, while only the chamfer threads on straight thread machine taps are cutting.
Regal Cutting Tools application specialists have been developing cutting designs for these distinct applications for many years. In today’s market the variables revolve around the following:
- Material being cut,
- Tool steel the taps are made from
- Wear resistant coating applied to the tools.
Standard sizes from 1/8” to 2” in diameter are available and because of the cutting differences in material being tapped, Regal offers styles including general purpose, high hook for softer materials, and low rake face cutting edge taps for tougher materials. An important design readily available is our interrupted thread taps, with every other thread removed to cut freely in stringy materials and produce good thread quality. Extension pipe taps will reach those tough to get at threading jobs, and short projection taps for special needs are available.