What Is a Drill Bit for 1/4 -18 NPT Tap?

To tap a 1/4-18 NPT (National Pipe Thread) hole, you will need a drill bit that is slightly smaller than the major diameter of the tap. The major diameter of a 1/4-18 NPT tap is 0.332 inches. Therefore, you will need a drill bit that is 0.320 inches in diameter.

It is important to use the correct size drill bit when tapping a hole, as using a bit that is too large will result in a weak thread that is more likely to fail. Conversely, using a bit that is too small will make it difficult to tap the hole and may damage the tap.

In addition to the drill bit, you will also need a tap wrench, tapping fluid, and a tapping guide. The tapping guide will help you to align the tap with the hole and ensure that you are tapping it straight. The tapping fluid will help to lubricate the tap and reduce friction, making it easier to tap the hole.

To tap a hole, first mark the location of the hole on the workpiece. Then, drill a hole using the appropriate drill bit. Next, apply some tapping fluid to the tap and insert it into the hole. Turn the tap wrench clockwise to begin tapping the hole. Be sure to apply steady pressure and turn the tap wrench slowly. As you tap the hole, periodically reverse the direction of rotation to break up the chips. Continue tapping until the tap has reached the desired depth.

Once you have tapped the hole, remove the tap and clean the threads with a brush. Apply some sealant to the threads and insert the desired fitting.