National Pipe Tapered Tap Chart (Recommended tap drill to use for 75% depth of thread)

To Tap This Size Pipe:

Use This Drill Bit:

(Closest Fractional:)

Decimal Inches:

1/8-27 NPT

Ltr.R

-

.3390

1/4-18 NPT

7/16"

7/16"

.4375

3/8-18 NPT

37/64"

37/64"

.5781

1/2-14 NPT

45/64"

45/64"

.7031

3/4-14 NPT

59/64"

59/64"

.9219

1-11 1/2 NPT

1 5/32"

1 5/32"

1.1562

1 1/4-11 1/2 NPT

1 1/2"

1 1/2"

1.5000

1 1/2-11 1/2 NPT

1 47/64"

1 47/64"

1.7344

2-11 1/2 NPT

2 7/32"

2 7/32"

2.2188