What Size Drill Bit for a 1-1/4” NPT Tap?

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The 1-¼” NPT tap is a pipe tap mainly used for re-threading damaged or jammed pipe threads. 1-¼” NPT taps are generally made of steel and are usable for both ferrous and non-ferrous materials. To know what size drill bit for a 1-¼” NPT tap is, read further.

What Size Drill Bit for a 1-1/4” NPT Tap?

A  1-¼” NPT Tap needs a drill bit size of 1 1/2 inches or 1.5 inches in decimals. NPT taps are also called pipe taps and don’t confuse them with NPTF taps and tapered taps like the 5/8-11 tap.

Woman in construction protective gear holding a cordless drill with her gloved hand

The NPT refers to the pipe and fittings with tapered threads that follow National Pipe Thread specifications much like the 1/4″ NPT with a bit size of 7/16″. If you plan to use NPT threads, do know they require a sealer like Teflon tape or pipe compound.

Here is a specification sheet to identify if you really are using a 1-¼” NPT tap:

  • Size: 1-¼ inch NPT
  • Material: carbon steel
  • Finish: uncoated (bright)
  • Style: NPT
  • Cutting direction: right hand
  • Tap size: 1-¼ NPT
  • Number of flutes: 5
  • Thread length: 1-¾ inches
  • Overall length: 4 inches
  • Shank size: 1.3125 inches
  • Matching drill bit: 1-31/64
  • Flute Type: NPT

Tips for Using Medium Drill Bits

Use a Test Board

When drilling wood or metal, your medium drill bits can create a splintered hole on one side. This is called a blowout which most amateur DIY workers get often. Blowouts can damage your workpiece affecting its quality.

It can sometimes lead to accidents since the drill bursting through the hole will make you lose control when you’re careless.

To stop this from happening, you can use a test or spare board as a cushion to clamp the piece down. The spare board prevents any blowouts since it acts as a cushion when drilling a hole.

Deburr the Hole

Most medium drill bits are used for drilling holes. So, deburring the hole is a sensible thing to do. After you’re done drilling, make sure the hole does not have sharp edges or burr left in the hole. Feel the hole until it’s smooth.

Man replacing a drill bit in a drill

It ensures your hole is smooth and clean, so you produce quality work. You can deburr a hole by running it in a bit of power and running the bit around the edges of the hole.

You can also use deburring tools to make the process simpler and easier. Most of them come with an instructional, so you should have no problems learning to properly use them.

Consider Using Stud Finder

A stud finder ensures you are not drilling into a water pipe or electric cables. Drilling through electric cables can create a huge accident, like electrocuting yourself. So, it’s best to use a stud finder as a safety precaution.

It’s also useful to avoid hitting water pipes which can cause leakage and flooding in your home. You should use a stud finder when drilling with hazardous materials near the drilling spot.

If you’re drilling into an unfamiliar surface, it’s best to use a stud finder to ensure you are drilling precisely and accurately. It’s better to be safe than sorry.


1-¼” NPT taps need a 1 1/2 inches size drill bit and can be used for re-threading damaged pipe threads. They’re mostly used for tapping fittings and couplings much like the 1/8″ NPT tap. If you’re going to use them, make sure to have a sealer for the threads.