7/8-20 UNEF Thread Specs
Standard: ASME B1.1 (UNEF)
Find the technical dimensions, threads per inch (TPI), and tapping guidelines for the 7/8-20 UNEF unified thread.
Compliant with the ASME B1.1 standard, this size has a nominal major diameter of 0.875 inches (22.23 mm) with a pitch of 0.05 inches (TPI of 20).
For general engineering or fastening, the standard recommended tap drill is 0.825 inches (20.96 mm) to achieve adequate thread engagement.
Dimensional Specifications (Inches & mm)
Size Designation
7/8-20 UNEF
Major Diameter (Nominal)
0.875 in(22.23 mm)
TPI (Threads per Inch)
20
Pitch
0.05 in
Pitch Diameter
0.8425 in(21.4 mm)
Minor Diameter (Ext)
0.8209 in(20.85 mm)
Minor Diameter (Int)
0.8263 in(20.99 mm)
Thread Height
0.0433 in
Drilling & Strength Specs
Tap Drill Size
0.825 in(20.96 mm)
Stress Area
0.5362 in²(345.95 mm²)
Quick Unit Converter
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Frequently Asked Questions
What is the tap drill size for 7/8-20 UNEF?
The recommended tap drill size for a 7/8-20 UNEF thread is 0.825 inches (approx. 20.96 mm) to achieve standard thread engagement.
How many threads per inch (TPI) does a 7/8-20 UNEF bolt have?
A standard 7/8-20 UNEF thread has exactly 20 threads per inch (TPI), with a corresponding linear pitch of 0.05 inches.
What is the major diameter of a 7/8-20 UNEF thread in millimeters?
The nominal major diameter of a 7/8-20 UNEF thread is 0.875 inches, which converts to 22.23 mm.