What Size Drill Bit for a 7/8-9 Tap?

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When it comes to re-threading damaged or jammed threads, ⅞- 9 taps are usually present and commonly used. If you don’t know what size drill bit for a ⅞- 9 tap is, continue reading. Although it’s usually shown in the packaging it comes with. If you want to make sure about the sizing, continue reading.

What Size Drill Bit for a 7/8-9 Tap?

A ⅞- 9 tap requires a size drill bit of 49/64 inches or 0.7656 inches in decimals. The ⅞- 9 tap is classified as NC or national course just like the 9/16- 12 tap. This means it’s a coarse thread or also known as UNC (Unified National Coarse).

Floor plan beside a drill, screws and other carpentry tools

UNC is the term commonly used in the United States and Canada. They have lesser threads per inch and are usually applied deeper compared to fine threads. ⅞- 9 taps are generally used for re-threading damaged or jammed threads.

It’s usually made out of carbon steel and in taper style like the 1-64 tap. The ⅞- 9 taps are mostly used in thru holes.

Tips for Using Large Drill Bits

Avoid Jamming Your Drill

One common thing when using large drill bits is jamming. It’s a common mistake amateur drillers make since they usually apply more pressure when drilling, which leads to jamming. You should learn how to avoid jamming your drill.

When you jam your drill, you might have to replace the tip, and your drill’s lifespan will shorten. You want to avoid spending more than you should when it’s avoidable. One thing you can do is not apply too much pressure when drilling.

Also, feel the drill and spot when you think it is slowing down. Pull it out when you think it’s slowing down and let it cool for a while, cleaning off any debris stuck in the drill.

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.

Various sizes and kinds of drill bits placed upright

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.

Don’t Use Excessive Force

Large drill bits naturally make people think that you have to use more power. However, that is not the case. It’s better to focus on precision instead of power. When drilling, you must hold the drill vertically at all times for consistency.

You want to hold a 90-degree angle while you let the bit drill for you. A slight bend could cause the hole to be unaligned, and the exit hole will not be where you want it to be.

It’s wise to not use excessive force that can affect your accuracy and stability when holding the drill.


⅞- 9 taps are part of the NC thread and its drill bit size can be usually found in most drill bit size charts. It’s part of the large drill bit size so it’s better to use a drill press for better accuracy.