2-1/4-4.5 UNC Thread Specs
Standard: ASME B1.1 (UNC)
Find the technical dimensions, threads per inch (TPI), and tapping guidelines for the 2-1/4-4.5 UNC unified thread.
Compliant with the ASME B1.1 standard, this size has a nominal major diameter of 2.25 inches (57.15 mm) with a pitch of 0.22222 inches (TPI of 4.5).
For general engineering or fastening, the standard recommended tap drill is 2.0278 inches (51.51 mm) to achieve adequate thread engagement.
Dimensional Specifications (Inches & mm)
Size Designation
2-1/4-4.5 UNC
Major Diameter (Nominal)
2.25 in(57.15 mm)
TPI (Threads per Inch)
4.5
Pitch
0.22222 in
Pitch Diameter
2.1057 in(53.48 mm)
Minor Diameter (Ext)
2.0094 in(51.04 mm)
Minor Diameter (Int)
2.0335 in(51.65 mm)
Thread Height
0.1925 in
Drilling & Strength Specs
Tap Drill Size
2.0278 in(51.51 mm)
Stress Area
3.2477 in²(2095.27 mm²)
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Frequently Asked Questions
What is the tap drill size for 2-1/4-4.5 UNC?
The recommended tap drill size for a 2-1/4-4.5 UNC thread is 2.0278 inches (approx. 51.51 mm) to achieve standard thread engagement.
How many threads per inch (TPI) does a 2-1/4-4.5 UNC bolt have?
A standard 2-1/4-4.5 UNC thread has exactly 4.5 threads per inch (TPI), with a corresponding linear pitch of 0.22222 inches.
What is the major diameter of a 2-1/4-4.5 UNC thread in millimeters?
The nominal major diameter of a 2-1/4-4.5 UNC thread is 2.25 inches, which converts to 57.15 mm.