5/8-18 UNF Thread Specs
Standard: ASME B1.1 (UNF)
Find the technical dimensions, threads per inch (TPI), and tapping guidelines for the 5/8-18 UNF unified thread.
Compliant with the ASME B1.1 standard, this size has a nominal major diameter of 0.625 inches (15.88 mm) with a pitch of 0.05556 inches (TPI of 18).
For general engineering or fastening, the standard recommended tap drill is 0.5694 inches (14.46 mm) to achieve adequate thread engagement.
Dimensional Specifications (Inches & mm)
Size Designation
5/8-18 UNF
Major Diameter (Nominal)
0.625 in(15.88 mm)
TPI (Threads per Inch)
18
Pitch
0.05556 in
Pitch Diameter
0.5889 in(14.96 mm)
Minor Diameter (Ext)
0.5649 in(14.35 mm)
Minor Diameter (Int)
0.5709 in(14.5 mm)
Thread Height
0.0481 in
Drilling & Strength Specs
Tap Drill Size
0.5694 in(14.46 mm)
Stress Area
0.256 in²(165.13 mm²)
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Frequently Asked Questions
What is the tap drill size for 5/8-18 UNF?
The recommended tap drill size for a 5/8-18 UNF thread is 0.5694 inches (approx. 14.46 mm) to achieve standard thread engagement.
How many threads per inch (TPI) does a 5/8-18 UNF bolt have?
A standard 5/8-18 UNF thread has exactly 18 threads per inch (TPI), with a corresponding linear pitch of 0.05556 inches.
What is the major diameter of a 5/8-18 UNF thread in millimeters?
The nominal major diameter of a 5/8-18 UNF thread is 0.625 inches, which converts to 15.88 mm.