What Size Drill Bit for a 2-1/2” NPT Tap?

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The 2-½” NPT tap is a common tap mainly used for cleaning or re-threading damaged or jammed pipes. 2-½” NPT taps are generally made of carbon steel and are usually heavier than most taps. If you want to know the size drill bit for a 2-½” NPT tap, read further.

What Size Drill Bit for a 2-1/2” NPT Tap?

A 2-½” NPT Tap needs a size drill bit of 2 5/8 inches or 2.625 inches in decimals. NPT taps are commonly called pipe taps. They are different from tapcons like the 3-16 tapcon.

Six gray drill bits placed in upright positions

NPT taps are commonly made of carbon steel and are generally used for cleaning or re-threading damaged or jammed pipe threads like the 1-1/4″ NPT. High-speed NPT pipes are for making new threads and for re-threading also.

You can use this NPT tap for threading a variety of materials both ferrous and non-ferrous. If you plan to use NPT threads, do know they require a sealer like Teflon tape or pipe compound.

Tips for Using Large Drill Bits

X Marks the Spot

When you’re drilling a pilot hole, it’s recommended to tape an X over the spot. You can use painter’s tape to mark it. The tape helps reinforce the wood or other surface to prevent cracking.

Cracking often happens with large drill bits since I’m handling big drilling projects. Reinforcing the surface isn’t bad when drilling since you don’t want cracks forming within your workpiece.

Aside from reinforcing with tape, you can also avoid cracking by drilling at the right depth. Drilling too much may cause cracking, so you must measure how deep you are drilling.

Keep a Spare Set of Drill Bits

You never know when your drill bit dulls or will last. So having spare sets help replace them immediately. Another benefit of using two sets of drill bits is you can alternate them, so you have a sharp one at the ready. 

Some professional drillers even use them at the same time. They use the new set of drills to drill a hole. The premise is that it keeps the sharper set for longer. After starting the hole, they switch to the old and sharpened set to finish the drilling making it less prone to dulling.

Man holding a green Bosch cordless drill

Learn the Proper Safety Precautions

When handling large drill bits, it’s important to practice safety to avoid accidents. You don’t know what might happen when drilling, or you might have overlooked something.

That’s why it’s not bad to learn about safety practices when drilling. Practice them and make it a habit when working on a drilling project.

One thing you can start with is wearing protective gear such as:

  • Drilling hand gloves
  • Masks
  • Safety glasses or goggles
  • Tight clothing

Starting with these and making it a habit to wear one will minimize the chance of accidents. Reading the manual before you start using the drill is also a great habit.


2-½” NPT taps need a large drill bit size of 2 5/8 inches and can be used for a wide range of materials. They’re mostly used for cleaning and re-threading. If you’re going to use them, make sure to have a sealer for the threads.