1-1/2-18 UNEF Thread Specs
Standard: ASME B1.1 (UNEF)
Find the technical dimensions, threads per inch (TPI), and tapping guidelines for the 1-1/2-18 UNEF unified thread.
Compliant with the ASME B1.1 standard, this size has a nominal major diameter of 1.5 inches (38.1 mm) with a pitch of 0.05556 inches (TPI of 18).
For general engineering or fastening, the standard recommended tap drill is 1.4444 inches (36.69 mm) to achieve adequate thread engagement.
Dimensional Specifications (Inches & mm)
Size Designation
1-1/2-18 UNEF
Major Diameter (Nominal)
1.5 in(38.1 mm)
TPI (Threads per Inch)
18
Pitch
0.05556 in
Pitch Diameter
1.4639 in(37.18 mm)
Minor Diameter (Ext)
1.4399 in(36.57 mm)
Minor Diameter (Int)
1.4459 in(36.73 mm)
Thread Height
0.0481 in
Drilling & Strength Specs
Tap Drill Size
1.4444 in(36.69 mm)
Stress Area
1.6419 in²(1059.3 mm²)
Quick Unit Converter
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Frequently Asked Questions
What is the tap drill size for 1-1/2-18 UNEF?
The recommended tap drill size for a 1-1/2-18 UNEF thread is 1.4444 inches (approx. 36.69 mm) to achieve standard thread engagement.
How many threads per inch (TPI) does a 1-1/2-18 UNEF bolt have?
A standard 1-1/2-18 UNEF thread has exactly 18 threads per inch (TPI), with a corresponding linear pitch of 0.05556 inches.
What is the major diameter of a 1-1/2-18 UNEF thread in millimeters?
The nominal major diameter of a 1-1/2-18 UNEF thread is 1.5 inches, which converts to 38.1 mm.