NPT National Pipe Thread Size

 Tap Drill Size (in.)

Decimal Equivalent (in.)

1/16 - 27

"C"

0.242

1/8 - 27

"Q" 

0.332

1/4 - 18

7/16

0.438

3/8 - 18

9/16

0.562

1/2 - 14

45/64

0.703

3/4 - 14

29/32

0.906

1.0 - 11�1/2

1�9/64

1.141

1�1/4 - 11�1/2

1�31/64

1.484

1�1/2 - 11�1/2

1�23/32

1.719

2.0 - 11�1/2

2�3/16

2.188

2�1/2 - 8

2�39/64

2.609

3.0 - 8

3�15/64

3.234