Measuring Trapezoidal Threads in 5 Steps: Diameter, Pitch, and Fit

Accurately measuring a trapezoidal thread is essential to ensure a proper fit between the lead screw (spindle) and the nut. Follow the steps below to determine the key specifications.

Step 1: Measure the Outer Diameter

The outer diameter can be measured using a caliper or a micrometer.

A small negative deviation is acceptable. For example, a measurement of 19.74 mm corresponds to a standard 20 mm spindle.

Step 2: Measure 5 or 10 Threads

Measure across 5 or 10 threads to determine the pitch. It is important to always measure from the same position on the thread profile.

If you start at the top-left edge of a thread, you must end at the top-left edge of the final thread in your count.

Measuring 10 threads is more accurate than measuring 5. Divide the total measured length by the number of threads to find the pitch per thread.

Step 3: Determine the Number of Starts (Single or Double Start)

Various terms are used for this, such as starts, leads, grooves, or single/double pitch.

Single-start: Most spindles are single-start, meaning the thread consists of one continuous groove with one starting point.

Double-start: These spindles have two separate starting points. You can identify a double-start spindle by looking at the end of the screw for two distinct entry points.

We describe a double pitch as follows: Trapezoidal Thread 24 x 10 P5

24 = Outer diameter

10 = Lead (travel distance per revolution in mm)

P5 = Pitch per thread (5 mm profile)

Step 4: Determine the Direction of Rotation

Hold the spindle vertically in front of you and look directly at the thread:

Does the thread climb upward to the left? Then it is a left-hand thread.

Does the thread climb upward to the right? Then it is a right-hand thread.

Step 5: Identify the Material

A simple magnet test can provide an initial indication of the material:

Strong, immediate attraction: The material is Steel.

No magnetic reaction: The material is Stainless Steel.

Weak/slight attraction: The material is typically a specific grade of Stainless Steel.

Please Note: Exceptions are possible. There are various grades and alloys within the categories of steel and stainless steel. This simple test cannot determine the exact specific material grade.

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Need Help Measuring?

Are you unsure about your measured diameter, pitch, or fit? Please feel free to contact us. Based on your measurements, we can help you identify the correct trapezoidal spindle or nut. If desired, you can also send a photo or drawing so we can provide specific advice.