7/8-9 UNC Thread Specs
Standard: ASME B1.1 (UNC)
Find the technical dimensions, threads per inch (TPI), and tapping guidelines for the 7/8-9 UNC 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 0.11111 inches (TPI of 9).
For general engineering or fastening, the standard recommended tap drill is 0.7639 inches (19.4 mm) to achieve adequate thread engagement.
Dimensional Specifications (Inches & mm)
Size Designation
7/8-9 UNC
Major Diameter (Nominal)
0.875 in(22.23 mm)
TPI (Threads per Inch)
9
Pitch
0.11111 in
Pitch Diameter
0.8028 in(20.39 mm)
Minor Diameter (Ext)
0.7547 in(19.17 mm)
Minor Diameter (Int)
0.7667 in(19.48 mm)
Thread Height
0.0962 in
Drilling & Strength Specs
Tap Drill Size
0.7639 in(19.4 mm)
Stress Area
0.4617 in²(297.89 mm²)
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Frequently Asked Questions
What is the tap drill size for 7/8-9 UNC?
The recommended tap drill size for a 7/8-9 UNC thread is 0.7639 inches (approx. 19.4 mm) to achieve standard thread engagement.
How many threads per inch (TPI) does a 7/8-9 UNC bolt have?
A standard 7/8-9 UNC thread has exactly 9 threads per inch (TPI), with a corresponding linear pitch of 0.11111 inches.
What is the major diameter of a 7/8-9 UNC thread in millimeters?
The nominal major diameter of a 7/8-9 UNC thread is 0.875 inches, which converts to 22.23 mm.