How do you measure thread pitch with calipers?

Measure along the axis from one crest to the next crest. For better accuracy, measure across several crests and divide by the number of gaps. Across five gaps, 25.0 mm means a 5 mm pitch and 25.4 mm means 5 threads per inch (5.08 mm).

How do you make a custom thread in Fusion 360?

Model a cylinder at the thread's minor diameter, then add a Coil around it with the measured pitch and a square section sized to twice the thread depth, positioned On Center and joined. Chamfer the coil edges to shape the flanks. Use Combine → Cut to make the mating part.

How do you find the minor diameter of a thread?

Measure the major diameter over the crests and the thread depth from crest to root on one side. Minor diameter = major diameter minus twice the depth. An 18 mm thread with 1.5 mm deep teeth has a 15 mm minor diameter.

How much clearance do 3D printed threads need?

On FDM, start by offsetting the female thread 0.2–0.4 mm (0.008–0.016 in) and test-print a short section. Leave the male part at the measured size and adjust only the female cut until it threads on by hand.

MeasuringPrecision & Reverse EngineeringReverse engineer threads

How do you model a non-standard thread you only have the physical part for?

You open Fusion's Thread tool and scroll the list. Metric, UNC, UNF, pipe. Not a single one matches the end of your paint pole, the neck of that bottle, or the housing you're trying to print a cap for. So you guess. And the guess either won't start or spins loose. Joseph Willis skips the list: four caliper readings, a Coil, a chamfer, done.

⚡ Rule of thumb

Measure four numbers off the real thread: major diameter, thread depth, pitch crest to crest, and tooth width at the root. Model a core at the minor diameter, wrap a square-section Coil around it at the measured pitch, then chamfer the coil edges into flanks. Cut the mating part from that model.

Starting point

Core = major − 2 × depth · Coil: diameter = core, pitch = measured, square section, On Center, Join

Measured

Major over the crests · depth crest to root, one side · pitch crest to next crest along the axis

Confidence

Creator technique

▶ Source video — How to Reverse Engineer Threads in Fusion — Joseph Williswatch on Facebook ↗

Applies to

Process: CAD reverse engineering for 3D printing (Autodesk Fusion)
Parts: Threads with no standard spec: paint and broom pole ends, bottle necks, odd housings and lids
Setup: Digital calipers; Fusion's Coil, Chamfer, Insert into Current Design, Joint and Combine → Cut
Orientation: Thread axis vertical in the model
Not for: Standard fasteners. If it's metric, UNC/UNF or pipe, use the Thread tool

Why it matters

The Thread tool only knows standard tables. Plenty of real threads aren't in them, and a thread that's almost right is just wrong. Close enough on diameter and off on pitch means it starts, then binds a turn and a half in.

Four numbers pin a coarse thread down completely. The core sets the root. The coil sets the pitch and how far the teeth stick out. The chamfer sets the flank.

And because you cut the mating part straight from the male model, the two halves match each other by construction, not by luck.

What good looks like

The model's outside diameter lands on the measured major diameter
Model pitch matches the part over several turns, not just one
The thread runs the same hand as the original
The printed part threads on by hand without binding

How to apply it

Measure the major diameter over the crests. In the clip: 18 mm.
Measure the thread depth, crest to root on one side, and subtract twice that from the major. In the clip: 1.5 mm deep, so 18 − 3 = 15 mm minor diameter.
Measure pitch crest to crest along the axis, and the tooth width at its root. In the clip: 5 mm pitch, a tooth about 3 mm wide (the calipers read 2.97).
Model the core as a cylinder at the minor diameter.
Add a Coil on the core: diameter = the minor diameter, pitch = your measured pitch, section Square, position On Center, operation Join. The clip uses 15 mm, −5 mm pitch and a 3 mm section.
Size the square to twice the thread depth. On Center buries half the section in the core, so a 3 mm square sticks out 1.5 mm and the outside lands back on 18 mm.
Chamfer the coil's edges with a two-distance chamfer to slope the square into flanks. The clip uses roughly 0.75 mm and 1.10 mm.
For the female part, insert the male design into the nut or cap design, joint it on center, and Combine → Cut to subtract the thread.
Print it and test it on the real part.

Test it on your setup

Print two or three turns first, not the whole cap. Minutes on the printer instead of hours.
Check the hand. It should thread on the same direction as the original. If it's backwards, flip the sign on the Coil pitch.
If it binds, open up the female cut. Offset its thread faces 0.2–0.4 mm (0.008–0.016 in) on FDM and reprint the slice. Leave the male model at the measured size.

Exceptions & tradeoffs

The clip doesn't show a clearance step. On FDM you'll almost always need one on the female thread, and 0.2–0.4 mm (0.008–0.016 in) is a sensible place to start.

A square section plus a chamfer is an approximation of a thread form, not the real profile. Great for coarse, low-load threads like poles, lids and jar necks. Not for anything that's a precision fastener.

Mind you, the tooth in the clip happens to be exactly twice the depth (3 mm wide, 1.5 mm deep), so one square size satisfies both. If yours isn't, size the square for the depth so the diameter is right, and use the chamfer to slim the tooth.

Watch for inch threads hiding as metric. A lot of US paint and broom poles are 3/4 in with 5 threads per inch, which is 5.08 mm pitch, not 5. That 0.08 mm stacks up to about 0.4 mm over five turns. Measure pitch across several crests and divide, and you'll catch it.

Common mistakes

Measuring pitch from a crest to the next root, and getting half the real numberMeasure crest to the next crest, one full thread
Setting the Coil diameter to the major diameterThe coil sits on the minor diameter, centered, so the section adds the depth outward
Printing a beautiful left-hand thread for a right-hand poleCheck the hand on the model and flip the pitch sign before printing
Printing the full part on the first tryPrint a two-turn slice and fit that first

Frequently asked questions

How do you measure thread pitch with calipers?Measure along the axis from one crest to the next crest. For better accuracy, measure across several crests and divide by the number of gaps. Across five gaps, 25.0 mm means a 5 mm pitch and 25.4 mm means 5 threads per inch (5.08 mm).
How do you make a custom thread in Fusion 360?Model a cylinder at the thread's minor diameter, then add a Coil around it with the measured pitch and a square section sized to twice the thread depth, positioned On Center and joined. Chamfer the coil edges to shape the flanks. Use Combine → Cut to make the mating part.
How do you find the minor diameter of a thread?Measure the major diameter over the crests and the thread depth from crest to root on one side. Minor diameter = major diameter minus twice the depth. An 18 mm thread with 1.5 mm deep teeth has a 15 mm minor diameter.
How much clearance do 3D printed threads need?On FDM, start by offsetting the female thread 0.2–0.4 mm (0.008–0.016 in) and test-print a short section. Leave the male part at the measured size and adjust only the female cut until it threads on by hand.

Joseph Willis (madebyjgwillis)Source & visual reference

Measuring an unknown thread with calipers (0:08–0:38), rebuilding it as a Coil (1:48) plus chamfer (2:12) in Fusion, and cutting the mating part (2:28) — How to Reverse Engineer Threads in Fusion ↗ at 0:08–2:48.

Summarized and independently edited by Start Here from Joseph Willis's reel, from sampled frames and the on-screen captions, no audio. The four-measurement method and the Coil, chamfer and Combine → Cut workflow are his. The 5 mm pitch comes from a hand-drawn annotation and the Coil dialog, and I've read the 2.97 mm caliper reading as the tooth width; the section size and chamfer values came off small UI text, so treat them as his example, not a spec. The twice-the-depth sizing note, the print clearance, the 5 TPI caution and the slice test are mine.