THREAD COMPARISON SHEET (BSP-NPT-UNF)

Angle and Seal Location
Thread Type Flank Angle Thread Angle Seal Location
BSP Parallel 55° 0° O-Ring /Gasket /Cone
BSPT Tapered 55° 1.47° On Thread
NPT Tapered 60° 1.47° On Thread
UNF/UNC Parallel 60° 0° O-Ring /Gasket /Cone
METRIC Parallel 60° 0° O-Ring /Gasket /Cone
Major Diameter (mm)
Thread Size BSP NPT UNF
1/16" 7.723 7.95
5/16" 7.938
1/8" 9.728 10.287
1/4" 13.157 13.716 6.35
3/8" 16.662 17.145 9.525
1/2" 20.955 21.336 12.7
3/4" 26.441 26.07 19.05
1" 33.249 33.401 25.4
TPI (Thread Per Inch )
Thread Size BSP NPT UNF
1/16" 28 27
5/16" 24
1/8" 28 27
1/4" 19 18 28
3/8" 19 18 24
1/2" 14 14 20
3/4" 14 14 16
1" 11 11-1/2 12

BSP THREAD

British Standard Pipe Threads Size Chart
( 55° Included angle )
Thread Diameter Threads Pitch Tapping Drill Size in mm
Size Inch mm per Inches [ mm ] G R
1/16" 0.3041 7.723 28 0.907 6.8 6.6
1/8" 0.383 9.728 28 0.907 8.8 8.6
1/4" 0.518 13.157 19 1.337 11.8 11.5
3/8" 0.656 16.662 19 1.337 15.25 15
1/2" 0.825 20.955 14 1.814 19 18.7
5/8" 0.902 22.911 14 1.814 21 20.7
3/4" 1.041 26.441 14 1.814 24.5 24.2
7/8" 1.189 30.201 14 1.814 28.25 28
1" 1.309 33.249 11 2.309 30.75 30.4

UNF THREAD

UNITIED NATIONAL FINE THREAD
( 60° Included angle )
Thread Diameter Threads per Inches Pitch Tapping Drill Size
Size Inch mm [ Inch ] [ mm ] For UNF thread [mm]
1/4" 0.25 6.35 28 0.907 5.5
5/16" 0.313 7.938 24 1.058 6.9
3/8" 0.375 9.525 24 1.058 8.5
7/16" 0.438 11.112 20 1.27 9.9
1/2" 0.5 12.7 20 1.27 11.5
9/16" 0.563 14.288 18 1.411 12.9
5/8" 0.625 15.875 18 1.411 14.5
3/4" 0.75 19.05 16 1.587 17.5
7/8 0.875 22.225 14 1.814 20.4
1 1 25.4 12 2.117 23.25

METRIC THREAD

ISO METRIC SCREW THREAD
( 60° Included Angle )
Thread Diameter Pitch Tapping Drill Size in mm
Size Inch mm [ mm ] [ mm ]
M6 0.236 6 1 5
M8 0.315 8 28 6.8
M10 0.394 10 19 8.5
M12 0.472 12 19 10.2
M14 0.551 14 14 12
M16 0.629 16 14 14
M18 0.709 18 14 15.50
M20 0.787 20 14 17.50

NPT THREAD

AMERICAN NATIONAL PIPE THREAD TAPER - NPT
( 60° Included Angle )
Thread Diameter Threads per Inches Pitch Tapping Drill Size
Size Inch mm [ Inch ] [ mm ] [ Inch ] [ mm ]
1/16" 0.313 7.95 27 0.9407 D
1/8" 10.287 8 27 0.9407 R 8.610
1/4" 13.716 10 18 1.411 7/16 11.113
3/8" 17.145 12 18 1.411 37/64 14.684
1/2" 21.336 14 14 1.814 23/32 18.256
3/4" 26.67 16 14 1.814 59/64 23.415
1" 33.401 18 11-1⁄2 2.209 1-5/32 29.369