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

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The 1 ½” NPT tap is a common tap mainly used for threading ferrous and non-ferrous materials. 1 ½” NPT taps are generally made of steel and are usually heavier than most taps If you want to know what size drill bit for a 1 ½” NPT tap is, read further.

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

A 1 ½” NPT Tap needs a size drill bit of 1 47/64 inches or 1.7344 inches in decimals. NPT taps are also called pipe taps, and don’t confuse them with NPTF taps and tapered taps like the 4-40 tap.

Drill, screws and toolbox placed on the floor

NPT taps can be carbon steel, HSS, or Interrupted thread NPT taps. Carbon steel NPT taps are generally used for cleaning or re-threading damaged or jammed pipe threads like the 1” NPT tap. High-speed NPT pipes are for making new threads and for re-threading also.

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.

Monitor Your Progress When Drilling

As you are drilling, check your work to see if there are any adjustments you need to do. If there are lugs or jams, remove it and clean them up. You can use the bit to clear the hole from debris

Man screwing metal detail on window with a drill

Make it a habit to pull out the drill bit every now and then and blow it off. This is important when you are drilling wood. Any flakes or chips of wood can get stuck in the bit.

The flakes and chips can make your drill bit heat up faster. This may be unnoticed by you. When your drill bit gets hot, it will function effectively less.

Keep A Spare Set of Drill Bits

You never know when your drill bit dulls or breaks. 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.


1 ½” NPT taps need a large drill bit size of 1 47/64 inches and can be used for a wide variety of materials. They’re mostly used for threading various materials. If you’re gonna use them, make sure to have a sealer for the threads.