1"-8 UNC Thread Specs
Standard: ASME B1.1 (UNC)
Find the technical dimensions, threads per inch (TPI), and tapping guidelines for the 1"-8 UNC unified thread.
Compliant with the ASME B1.1 standard, this size has a nominal major diameter of 1 inches (25.4 mm) with a pitch of 0.125 inches (TPI of 8).
For general engineering or fastening, the standard recommended tap drill is 0.875 inches (22.23 mm) to achieve adequate thread engagement.
Dimensional Specifications (Inches & mm)
Size Designation
1"-8 UNC
Major Diameter (Nominal)
1 in(25.4 mm)
TPI (Threads per Inch)
8
Pitch
0.125 in
Pitch Diameter
0.9188 in(23.34 mm)
Minor Diameter (Ext)
0.8647 in(21.96 mm)
Minor Diameter (Int)
0.8782 in(22.31 mm)
Thread Height
0.1083 in
Drilling & Strength Specs
Tap Drill Size
0.875 in(22.23 mm)
Stress Area
0.6057 in²(390.8 mm²)
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Frequently Asked Questions
What is the tap drill size for 1"-8 UNC?
The recommended tap drill size for a 1"-8 UNC thread is 0.875 inches (approx. 22.23 mm) to achieve standard thread engagement.
How many threads per inch (TPI) does a 1"-8 UNC bolt have?
A standard 1"-8 UNC thread has exactly 8 threads per inch (TPI), with a corresponding linear pitch of 0.125 inches.
What is the major diameter of a 1"-8 UNC thread in millimeters?
The nominal major diameter of a 1"-8 UNC thread is 1 inches, which converts to 25.4 mm.