🔧 Buttress Thread Pitch Calculator
Calculate pitch, lead, minor diameter, pitch diameter, thread depth & more for buttress threads (7°/45° or 3°/30° flanks)
| Nominal Size | TPI | Pitch (in) | Major Dia (in) | Pitch Dia (in) | Minor Dia (in) | Thread Height (in) |
|---|---|---|---|---|---|---|
| 1/4" | 16 | 0.0625 | 0.250 | 0.2094 | 0.1938 | 0.0375 |
| 5/16" | 14 | 0.0714 | 0.3125 | 0.2676 | 0.2500 | 0.0429 |
| 3/8" | 12 | 0.0833 | 0.375 | 0.3249 | 0.3050 | 0.0500 |
| 1/2" | 10 | 0.1000 | 0.500 | 0.4437 | 0.4188 | 0.0600 |
| 5/8" | 8 | 0.1250 | 0.625 | 0.5563 | 0.5250 | 0.0750 |
| 3/4" | 6 | 0.1667 | 0.750 | 0.6500 | 0.6125 | 0.1000 |
| 1" | 5 | 0.2000 | 1.000 | 0.8812 | 0.8438 | 0.1200 |
| 1-1/4" | 5 | 0.2000 | 1.250 | 1.1312 | 1.0938 | 0.1200 |
| 1-1/2" | 4 | 0.2500 | 1.500 | 1.3563 | 1.3125 | 0.1500 |
| 2" | 4 | 0.2500 | 2.000 | 1.8563 | 1.8125 | 0.1500 |
| Nominal Size | Pitch (mm) | Major Dia (mm) | Pitch Dia (mm) | Minor Dia (mm) | Thread Height (mm) | Root Radius (mm) |
|---|---|---|---|---|---|---|
| M10 | 2.0 | 10.000 | 8.701 | 7.835 | 1.200 | 0.200 |
| M12 | 2.0 | 12.000 | 10.701 | 9.835 | 1.200 | 0.200 |
| M16 | 2.5 | 16.000 | 14.376 | 13.294 | 1.500 | 0.250 |
| M20 | 2.5 | 20.000 | 18.376 | 17.294 | 1.500 | 0.250 |
| M24 | 3.0 | 24.000 | 22.051 | 20.752 | 1.800 | 0.300 |
| M30 | 3.5 | 30.000 | 27.727 | 26.211 | 2.100 | 0.350 |
| M36 | 4.0 | 36.000 | 33.402 | 31.670 | 2.400 | 0.400 |
| M48 | 5.0 | 48.000 | 45.003 | 43.088 | 3.000 | 0.500 |
| Material | SFM Range | Chip Load / Pass (in) | Passes (Rough) | Passes (Finish) | Coolant |
|---|---|---|---|---|---|
| Mild Steel | 60 – 100 | 0.003 – 0.006 | 5 – 8 | 1 – 2 | Cutting oil |
| Alloy Steel | 40 – 80 | 0.002 – 0.004 | 6 – 10 | 2 – 3 | Sulfurized oil |
| Stainless (304) | 30 – 60 | 0.001 – 0.003 | 8 – 12 | 2 – 3 | Flood coolant |
| Aluminum 6061 | 200 – 400 | 0.005 – 0.010 | 3 – 5 | 1 | Dry / air blast |
| Brass / Bronze | 100 – 200 | 0.004 – 0.008 | 4 – 6 | 1 – 2 | Dry / mist |
| Cast Iron | 50 – 80 | 0.003 – 0.005 | 5 – 8 | 1 – 2 | Dry |
| Titanium | 20 – 40 | 0.001 – 0.002 | 10 – 15 | 3 – 4 | Flood + high pressure |
| Acetal / Nylon | 300 – 600 | 0.008 – 0.015 | 2 – 3 | 1 | Dry / air |
| Application | Typical Size | Flank Angle | Material | Lead Type | Note |
|---|---|---|---|---|---|
| Hydraulic cylinder rod | 1" – 3" | 7° / 45° | Alloy steel | Single | High axial load capacity |
| Screw jack / lifting | 1-1/2" – 4" | 7° / 45° | Mild/alloy steel | Single/Double | One-direction thrust |
| Injection mold clamp | M30 – M80 | 3° / 30° | Tool steel | Single | Precision fit required |
| Vise spindle | 3/4" – 1-1/2" | 7° / 45° | Mild steel | Single | Standard shop vise |
| Arbor press ram | 1" – 2" | 7° / 45° | Cast iron / steel | Single | Downward force only |
| Feed screw (CNC) | M20 – M40 | 3° / 30° | Alloy steel | Double/Triple | Fast traverse, high load |
| Wood splitting wedge | 1" – 1-1/2" | 7° / 45° | Mild steel | Single | Low precision tolerance |
A buttress thread has quite a different form when one compares it with average threads. It sticks out because of its uneven profile, that allows it to well control loads in one direction, although it less works in the opposite direction. The resistance on the load-bearing side stays fairly low, so the thread fits to last big force.
But if one flips it, then the resistance grows and the skill to bear load quickly drops. That one-way feature explains why one commonly uses them in press systems and levers, where the force chiefly acts mainly.
Buttress Thread: Shape, Uses and How to Measure
One advantage of a buttress thread is its good deal with other kinds of threads. They need fewer efforts to make than square threads yet they last bigger load than angled threads of same size. Like this they fill well the middle position between those two types.
The standard form of a buttress thread has a 7-degree corner on one side and 45 degrees on the other. The 7-degree side (the close or tight side). One finds almost straight, almost direct to the axis.
It is the main part, that resists the main load. The depth of the thread reaches around 0.6 times the step, while the flat part of the back measures about 0.1631 times the step. If you see a label PUSH-PUSH, it points that the outer thread pushes, with the 7-degree load side forward and the 45-degree back side following behind.
There also exists a different variant in some standards. Standard DIN 513 describes a 3-degree and 30-degree form of buttress thread, sometimes called sawtooth-thread. In Italy one calls it “filettatura dente di sega“, while in Germany it is “Sagengewinde”.
One even meets designs with a 0-degree side combined with 5 degrees on the other, together with flat parts at the root and back in a one-corner part of the step.
The length of a metric buttress thread one guesses at around 10 mm until 300 mm based on the size. The step ranges somewhere from 2 mm until 24 mm, based on the diameter. Do not forget to check the main diameter, pitch diameter, root diameter and all there tolerances and gaps.
To measure correctly the pitch diameter of a buttress thread needs real attention. The old method uses wires or balls, that rest against the sides, with math based on the corners of those sides. Some modern tools skip the math for outer threads, simply hitting directly the pitch diameter.
The thread length is simply step times the number of starts, but to reach the right form needs careful control, measuring the width of the thread at the base and so on. But hear the main point: the pitch diametergenuinely matters more than precise shape of that corner.
