ThreadCalc.com
Precision Thread Calculator
External Dimensions
Allowance
Flat At Root (Opt)
Height (Basic)
0.2500-20 UNC-2A
Major Diameter
Max
Min
Mean
Pitch Diameter
Max
Min
Tol
Minor Diameter
Max
Min (ref)
Root Radius
Max
Min
Internal Dimensions
Flat At Root (Opt)
Height (Basic)
0.2500-20 UNC-2B
Minor Diameter
Min
Max
Mean
Pitch Diameter
Min
Max
Tol
Major Diameter
Min
Max (ref)
Thread Types and Sizes
Sizes
Unified Series 60°
Acme 29°
Buttress 7° x 45°
UNM Miniature 60°
NPT Taper Pipe 60°
NPTF Dryseal Taper Pipe 60°
NPSM Straight Pipe 60°
NPSL Straight Pipe 60°
STI Threaded Insert 60°
────────────
ISO Series 60°
ISO Trapezoidal 30°
ISO Buttress 3° x 30°
Whitworth 55°
BA British Association 47.5°
BSPT Taper Pipe 55°
BSPP Parallel Pipe 55°
ISO Threaded Insert 60°
Pg Conduit Thread 80°
Major (Inch)
TPI
UN
UNR
UNJ
RH
LH
?
Classes of Fit
External
1A
2A
3A
Internal
1B
2B
3B
Measurement Over Wires (3 Wire)
Max
Min
Wire Diameters
Constants
Max
Best
Best
Min
Alternate
Alternate
?
Starts - Pitch - Lead - Lead Angle
Starts
1
2
3
4
5
6
7
8
Pitch
Lead
Lead Angle
?
Percent Thread
Percent
Minor Dia
50% = 0.2229
55% = 0.2202
60% = 0.2175
65% = 0.2148
70% = 0.2121
75% = 0.2094
80% = 0.2067
85% = 0.2040
Tap Drills
Cut Tap
Form Tap
Inch
Metric
Diameter
5.10mm
5.10mm
0.2008
7
5.11mm
0.2010
5.15mm
5.15mm
0.2028
13/64
5.16mm
0.2031
6
5.18mm
0.2040
5.20mm
5.20mm
0.2047
5
5.22mm
0.2055
5.25mm
5.25mm
0.2067
5.30mm
5.30mm
0.2087
4
5.31mm
0.2090
5.35mm
5.35mm
0.2106
5.40mm
5.40mm
0.2126
3
5.41mm
0.2130
5.45mm
5.45mm
0.2146
5.50mm
5.50mm
0.2165