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ASTM D412 
Rubber Tensile Test Fixture

Universal Grip ASTM D412 specimen cutter for universal testing machines

Downloads: Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers - PDF · ASTM D412 Specimen Cutter – Universal Grip Data Sheet (PDF)

Cutting dies for ASTM D412: Die A · Die B · Die C · Die D (hardened or ribbon steel, with data sheets)

Non-contact strain measurement: UGC-VE-2105 5 MPx video extensometer · all UGC-VE models

Written by Chris Thomas, Universal Grip Company · Reviewed by Frank Bertini · Updated October 17, 2026

ASTM D412 is the standard test method for the tensile properties of vulcanized rubber and thermoplastic elastomers. A dumbbell (Method A) or a cut ring (Method B) is stretched to failure at 500 mm/min while the force and elongation are recorded, giving tensile strength, stress at a stated elongation (the rubber industry's "modulus"), ultimate elongation and tensile set. It is the first test run on nearly every rubber compound: tire, seal, hose, belt, footwear, glove, medical and consumer-goods specifications all set limits against it, and it is the companion to ASTM D624 tear and D2240 hardness in a basic rubber lab.

This guide gives the full table of all six dies, the thickness the standard actually calls for (2.0 ± 0.2 mm, not the 3 mm that several equipment pages quote), the ring specimens, the test speed and the conditioning rules from D1349 rather than the plastics practice D618, how to grip rubber without slippage or jaw breaks, why elongation must come from bench marks or an extensometer and never from crosshead travel, all four calculations with a worked example and the median-of-three rule, the tensile set procedure, and how D412 compares with ISO 37 and DIN 53504. It ends with the dies, grips, extensometers and machines Universal Grip supplies for the test.

In this guide: What ASTM D412 Measures · Method A Dumbbell Specimens: Dies A to F · Method B Ring Specimens · Specimen Preparation and Cutting Dies · Conditioning: D1349, Not D618 · Test Speed and Machine Requirements · Grips, Slippage and Jaw Breaks · Extensometers and Bench Marks · Step-by-Step Procedure (Method A) · Calculations and Worked Example · Tensile Set Procedure · ASTM D412 vs ISO 37 vs DIN 53504 · Common Errors · Equipment for ASTM D412 · FAQ

What ASTM D412 Measures

D412 covers the tensile properties of thermoset rubber and thermoplastic elastomers in the form of molded sheet, extruded or molded product and cut rings. Hard rubber (ebonite) and rigid plastics are excluded; they go to ASTM D638. The method reports four properties, with terminology from ASTM D1566:

  • Tensile strength: the maximum tensile stress reached while stretching the specimen to rupture, in MPa or psi, based on the original cross-section.

  • Tensile stress at a given elongation (M100, M200, M300 and so on, called modulus in the rubber trade): the stress at 100 %, 200 % or 300 % elongation. It is not an elastic modulus; it is the stress needed to reach that strain and is the best single indicator of the state of cure and filler loading.

  • Ultimate elongation: the elongation at rupture, as a percentage of the original bench-mark or gauge length.

  • Tensile set: the residual extension, as a percentage of the original length, after the specimen has been stretched to a stated elongation, held, released and allowed to recover, or after break.

Rubber stretches to several hundred percent and thins as it does, and its stress-strain curve is non-linear from the start, so none of the plastics or metals conventions (yield, 0.2 % offset, Young's modulus) apply. That is why the rubber method has its own specimen shapes, its own speed and its own definitions. Our elastomers testing page gives the lab overview; this guide covers the standard itself.

Method A Dumbbell Specimens: Dies A to F

Method A uses dumbbell specimens cut from sheet with one of six dies. The dimensions below are the nominal values from the standard's Figure 1 (in millimetres): overall length, narrow (neck) section length, tab width, neck width, and the bench-mark gauge length. Tolerances on neck width are +0.05 mm, on tab width ± 1 mm, on neck length ± 2 mm and on gauge length ± 0.25 mm (25 mm) or ± 0.5 mm (50 mm).

  • Die A: 140 overall, 59 neck, 25 tab, 12 neck width, 50 gauge. The wide-neck die for soft, low-strength compounds where a 6 mm neck gives too little force.

  • Die B: 140 overall, 59 neck, 25 tab, 6 neck width, 50 gauge. Same long neck as A with the 6 mm width; used where a 50 mm gauge is wanted on a standard compound.

  • Die C: 115 overall, 33 neck, 25 tab, 6 neck width, 25 gauge. The default die in almost every specification and the one most published data refer to.

  • Die D: 100 overall, 33 neck, 16 tab, 3 neck width, 25 gauge. The small die for thin sheet, small molded parts and limited material; results differ from Die C.

  • Die E: 125 overall, 59 neck, 16 tab, 3 neck width, 50 gauge. Narrow long neck for small parts where a 50 mm gauge is needed.

  • Die F: 125 overall, 59 neck, 16 tab, 6 neck width, 50 gauge. The 6 mm neck with narrow tabs, for cutting from narrow strips or products.

Thickness. Dumbbells are cut from sheet 2.0 ± 0.2 mm (0.08 ± 0.008 in) thick; the standard permits 1.3 to 3.3 mm, and anything outside the 2.0 mm standard must be reported, because tensile strength and elongation both change with thickness. Several widely read equipment pages say Die C is 3 mm thick; that is the upper end of the permitted range, not the standard, and specimens at 3 mm give different numbers from those at 2 mm. Measure thickness per ASTM D3767 with a pressure-foot gauge at three points along the neck and use the median; the cross-section is the die neck width multiplied by the median thickness.

Straight specimens. Where a dumbbell cannot be cut, for example from a narrow extruded profile or a thin cord, the standard allows straight strips of uniform cross-section, with the understanding that most will break in the grips; use them only when the specification allows and report the shape.

Choosing a die. Follow the specification first. Otherwise: Die C for sheet and most products, Die D when material is limited or parts are small, Die A for very soft compounds that give too little load on a 6 mm neck, and Dies B, E and F when a 50 mm gauge length is wanted for extensometer resolution. Never compare Die C data with Die D data from another lab; the narrower neck gives higher strength and elongation on most compounds.

Method B Ring Specimens

Method B uses rings cut from sheet or tube with a rotating-blade cutter. Type 1 rings have an inside circumference of 50 mm (inside diameter 15.9 mm, outside 17.9 mm) and a radial width of 1.0 mm; Type 2 rings have an inside circumference of 100 mm (ID 31.8 mm, OD 35.8 mm) and a radial width of 2.0 mm. Thickness is 1 to 3.3 mm, measured as for dumbbells. The ring is mounted over two spindles of equal diameter, one of which is driven; the spindles rotate during the test to distribute the stretch, and elongation is calculated from spindle separation and the ring's internal circumference. Type 1 rings are tested at 500 ± 50 mm/min; Type 2 rings at 1,000 ± 100 mm/min, so that the strain rate at the inner surface is comparable. Rings avoid the die-edge and grip problems of dumbbells and suit automated and high-throughput testing, but their results are not interchangeable with Method A.

O-ring tensile testing per ASTM D1414 uses the same spindle principle on finished O-rings; our O-ring tensile system guide covers the fixture, spindle sizing and speed for that method.

Specimen Preparation and Cutting Dies

  • Prepare sheet per ASTM D3182 and D3183 (mixing, molding and sheet preparation) with the grain direction marked; cut dumbbells with the neck parallel to the grain unless the specification says otherwise, and report the direction. Cross-grain specimens from calendered sheet give measurably lower elongation.

  • Cut with a sharp ASTM D412 die in a single stroke on a die press or arbor press, on a hard flat cutting pad. A dull die leaves a ragged neck edge that starts tears and lowers both strength and elongation; a die sharpener and a reference compound keep it in check.

  • Inspect the neck under light; discard specimens with nicks, voids, flash or uneven thickness. Wipe dies on tacky compounds with a soap solution.

  • Apply bench marks 25 mm (Dies C and D) or 50 mm (A, B, E, F) apart on the neck with a stamp or a marking tool and a flexible ink that does not damage the surface; if a video extensometer is used, high-contrast marks or targets serve the same purpose.

Conditioning: D1349, Not D618

D412 refers to ASTM D1349 for standard temperatures, not to the plastics conditioning practice D618. The rules are: store vulcanizates for at least 16 hours after vulcanization before testing; condition specimens for at least 3 hours at 23 ± 2 °C (73.4 ± 3.6 °F) before cutting and testing; for compounds known to be affected by humidity, condition at 50 ± 5 % relative humidity for at least 24 hours. Pages that quote the D618 default of 40 hours at 50 ± 5 % RH are applying the plastics rule; it is not wrong to exceed the rubber requirement, but it is not what D412 asks for, and humidity control is only needed for moisture-sensitive compounds such as some polyurethanes and polyamide-based TPEs.

For tests at elevated or sub-ambient temperatures, use the D1349 standard temperatures (−70 to +250 °C series), soak the specimen in an environmental chamber until it reaches equilibrium (a 2 mm specimen needs about 3 to 5 minutes once the chamber is stable; the grips need longer), and test in the chamber. Rubber properties are strongly temperature-dependent, so a specimen tested a minute after leaving a cold chamber is not at the test temperature.

Test Speed and Machine Requirements

The crosshead speed is 500 ± 50 mm/min (20 ± 2 in/min) for all dumbbells and Type 1 rings, and 1,000 ± 100 mm/min for Type 2 rings, maintained to rupture. The speed must be held under load: a 500 % elongation on a Die C specimen means the grips separate by more than 300 mm, and the machine needs that stroke plus the initial grip separation (about 65 mm for Die C). A frame with at least 500 mm of travel, and 1,000 mm or more for high-elongation compounds and Die A/B specimens, is the practical minimum.

  • Load accuracy: within ± 2 % of reading over the range used; aim for ± 1 %. Rubber loads are low (a Die C specimen at 15 MPa breaks at about 180 N), so a 500 N to 2 kN cell suits most compounds and a 5 kN cell is only for very high-strength or thick specimens.

  • Speed accuracy: within the ± 10 % stated; verify at the top speed with a stopwatch or the controller's encoder.

  • Elongation measurement: by bench marks and a scale, by a contact extensometer that can follow several hundred percent strain, or by a video extensometer. Crosshead displacement is not acceptable for elongation, because the tabs and the neck shoulders stretch too; a crosshead-based elongation on Die C can overstate the true value by 30 to 60 %.

  • Data rate: 50 Hz or more, so the rupture peak is captured; rubber fails abruptly.

A Mark-10 tensile tester with a 500 N or 1 kN cell and the long-travel column runs Die C and D specimens on most compounds; the 1,500 lb model covers high-strength compounds. For a full rubber lab, a 2.5 kN or 5 kN benchtop UTM with 1,000 mm of travel and a video extensometer runs every D412 specimen and D624 tear on the same frame.

Grips, Slippage and Jaw Breaks

Rubber thins as it stretches, so an ordinary vise grip loses its clamping force during the test and the tab creeps out, giving a load trace that plateaus or sawtooths and an elongation that is wrong. The standard requires grips that hold the specimen without slipping and load it along its axis. Three designs do that:

  • Pneumatic grips: constant air pressure maintains the clamping force as the tab thins; parallel-closing jaws insert the specimen square. The first choice for a production rubber lab, with 25 mm rubber-faced or lightly serrated jaws for Dies A to C and 16 mm or narrower jaws for D to F.

  • Roller (eccentric) grips: self-tightening by geometry, so the clamping force rises with the pull; the usual grip on small testers without an air supply and for very soft compounds that pneumatic jaws can cut.

  • Wedge grips: mechanical self-tightening; heavier than needed for most rubber, but useful for straight strips and thick specimens on a universal testing machine.

Jaw breaks and failure location

A specimen that breaks at the tab, at the jaw edge or in the shoulder outside the bench marks has not been tested; D412 requires that such results be discarded and the test repeated with another specimen, since the stress at the jaw is not the stress in the neck. Jaw breaks come from serrations cutting the tab, from over-clamping, from the specimen being inserted at an angle so one edge of the tab carries the load, or from the jaw edge sitting on the shoulder radius. Fixes, in order: insert the tab fully and square with the shoulder clear of the jaw, use flat rubber faces or fine serrations at a moderate air pressure, and align the grips so the specimen axis is on the load line. Grip the tab symmetrically with the same insertion depth top and bottom; a tilted specimen also skews the strain field that an extensometer sees.

All of our rubber grips are supplied in the adapter for Instron, MTS, ZwickRoell, Shimadzu, Mark-10 and other machines; see tensile grips for the full range.

Extensometers and Bench Marks

Elongation is defined on the bench marks, 25 mm apart on Dies C and D and 50 mm on the others. The standard allows reading the marks against a scale by eye during the test, which is how the test was run for decades and is still acceptable; the operator reads the separation at rupture and at the elongations where stress is wanted. A contact extensometer with long-travel arms can follow the marks automatically but adds mass to a specimen that is already thinning, and its knife edges can start a tear on soft compounds. A non-contact video extensometer is now the usual answer: it tracks the two marks or printed targets to rupture with no contact, resolves the strain at 100 and 300 % accurately, and records the whole curve. Our video extensometers and XL long-travel extensometers are both used for D412; the guide to choosing an extensometer compares them.

Whichever method is used, the stress at a given elongation must be read at the elongation of the marks, not of the crosshead. A compound with a true M100 of 2.0 MPa will show about 1.5 MPa if 100 % crosshead-based strain is used, because the crosshead has to travel further than the neck stretches.

Step-by-Step Procedure (Method A)

  • 1. Cut three dumbbells per material in the grain direction specified, inspect, and apply bench marks.

  • 2. Measure thickness at three points in the neck (median) and record the die neck width; compute the original cross-section A0.

  • 3. Mount the specimen square in self-tightening grips with equal tab insertion and the bench marks centred between the jaws; zero the load.

  • 4. Set 500 mm/min and start the extensometer or scale reading on the bench marks.

  • 5. Stretch to rupture, recording force continuously and the bench-mark separation at the specified elongations (100 %, 200 %, 300 %) and at rupture.

  • 6. Check the break location. Discard and replace any specimen that broke outside the bench marks or at a flaw.

  • 7. Calculate tensile strength, stress at each elongation and ultimate elongation for each specimen, and report the median of three. If the specification calls for tensile set, run that as a separate procedure (below).

Calculations and Worked Example

  • Tensile strength: TS = F max ÷ A0, with F max in newtons and A0 the original neck cross-section (width × median thickness) in mm², giving MPa (multiply by 145 for psi).

  • Tensile stress at a given elongation: M100 = F at 100 % ÷ A0, and likewise M200, M300. Always on the original area.

  • Ultimate elongation: E = (L − L0) ÷ L0 × 100, where L0 is the original bench-mark distance and L the distance at rupture.

  • Tensile set: set = (L2 − L0) ÷ L0 × 100, where L2 is the bench-mark distance after the specified stretch, hold and recovery.

Worked example (Die C). Neck width 6.0 mm, thickness readings 2.02, 1.98, 2.00 mm (median 2.00 mm), so A0 = 12.0 mm². Bench marks 25.0 mm. The force at 100 % elongation (marks at 50.0 mm) is 24 N; at 300 % (100.0 mm) it is 96 N; at rupture the force is 180 N and the marks are 137 mm apart. Tensile strength = 180 ÷ 12.0 = 15.0 MPa (2,175 psi). M100 = 24 ÷ 12.0 = 2.0 MPa; M300 = 96 ÷ 12.0 = 8.0 MPa. Ultimate elongation = (137 − 25) ÷ 25 × 100 = 448 %. The other two specimens give 14.6 MPa / 430 % and 15.3 MPa / 455 %; the reported values are the medians, 15.0 MPa and 448 %.

Reporting. D412 reports the median of three specimens for each property, not the mean, because occasional low values from edge flaws skew a mean. Report the die, thickness, grain direction, conditioning, speed, elongation method, test temperature and the individual values if required. A coefficient of variation under 5 % on tensile strength and under 8 % on elongation is normal for a good compound and a sharp die; wider scatter usually means die edge, grain or jaw problems rather than the compound.

Tensile Set Procedure

Tensile set measures how much a compound fails to recover after being stretched, which is what a gasket or a band experiences in service. The standard procedure stretches the specimen at the standard speed to a specified elongation (commonly 100 %, or as the specification requires), holds it for 10 minutes, releases it quickly, lets it recover for 10 minutes on a flat surface, and then measures the bench-mark distance. Set is reported as the percentage increase over the original bench-mark length. A second form, set after break, fits the two halves of a ruptured specimen together 10 minutes after the test and measures the bench-mark distance across the join, which gives a set value from the same specimen used for strength. State which procedure and which elongation were used; results from the two are not the same.

ASTM D412 vs ISO 37 vs DIN 53504

  • ISO 37: the international rubber tensile standard; Type 1 and Type 2 dumbbells (Type 1 is 115 mm long with a 6 mm neck and 25 mm gauge, close to Die C; Type 2 is 75 mm with a 4 mm neck and 20 mm gauge), plus Types 3 and 4 for small specimens, and ring specimens; 500 mm/min; thickness 2.0 ± 0.2 mm. Close to D412 but with its own die tolerances and its own reporting (median of three or five), so the two are not formally interchangeable.

  • DIN 53504: the German method with S1, S2, S3 and S3A dumbbells; S1 corresponds to Die C and ISO 37 Type 1, S2 to ISO Type 2; 200 mm/min is common in older specifications, so check the rate before comparing.

  • ASTM D638: rigid and semi-rigid plastics at 5 to 500 mm/min with its own specimen types; use it for hard TPEs above about 90 Shore A or any material that yields.

Die C, ISO 37 Type 1 and DIN S1 are near enough that one cutting die often serves all three, but the thickness and speed must match the standard being reported.

Common Errors

  • Sheet at 3 mm instead of 2.0 ± 0.2 mm, or thickness not reported when it differs from 2.0 mm.

  • Elongation taken from crosshead displacement, overstating it by a third or more.

  • Stress at 100 or 300 % read at crosshead-based strain, understating M100 and M300.

  • Grips that slip (vise grips), seen as a plateau or sawtooth before rupture.

  • Jaw breaks counted as results instead of being discarded and repeated.

  • Dull die or cross-grain cutting without reporting the direction.

  • Conditioning per D618 (40 hours) assumed required; or specimens tested within 16 hours of vulcanization.

  • Reporting the mean of three instead of the median.

  • Machine travel too short for high-elongation compounds, ending the test before rupture.

  • Mixing Die C and Die D data, or D412 and ISO 37 data, in one comparison.

Equipment for ASTM D412

For a fuller discussion of dies, grips and extensometers for this test, see our article on ASTM D412 rubber tensile testing; the tear companion is covered in the ASTM D624 guide.

ASTM D412 FAQ

What is ASTM D412?

The ASTM standard test method for tensile properties of vulcanized rubber and thermoplastic elastomers. Dumbbell (Method A) or ring (Method B) specimens are stretched to rupture at 500 mm/min to determine tensile strength, stress at a given elongation, ultimate elongation and tensile set.

What are the ASTM D412 Die C dimensions?

115 mm overall length, 33 mm neck length, 25 mm tab width, 6 mm neck width and 25 mm bench marks, cut from sheet 2.0 ± 0.2 mm thick (1.3 to 3.3 mm permitted). Die C is the default specimen in most specifications.

What is the test speed for ASTM D412?

500 ± 50 mm/min (20 ± 2 in/min) for all dumbbells and Type 1 rings, maintained to rupture; Type 2 rings run at 1,000 ± 100 mm/min.

How thick should an ASTM D412 specimen be?

2.0 ± 0.2 mm (0.08 ± 0.008 in) is the standard thickness; 1.3 to 3.3 mm is permitted and must be reported. The 3 mm figure quoted on some sites is the upper limit, not the standard.

How is tensile strength calculated in ASTM D412?

Maximum force divided by the original cross-section of the neck (die neck width × median thickness), in MPa. Stress at 100 % or 300 % elongation uses the force at that elongation on the same original area.

What is modulus at 100 % or 300 % in ASTM D412?

The tensile stress at that elongation, called M100 or M300. It is not an elastic modulus; it is the stress needed to stretch the specimen to 100 % or 300 % and is used as a measure of cure state and reinforcement.

How is elongation measured in ASTM D412?

From bench marks 25 mm (Dies C and D) or 50 mm (A, B, E, F) apart on the neck, read with a scale, a long-travel extensometer or a video extensometer. Crosshead displacement is not acceptable because the tabs and shoulders also stretch.

How many specimens does ASTM D412 require?

Three per material, with the median of the three reported for each property. Specimens that break outside the bench marks (jaw breaks) are discarded and replaced.

What conditioning does ASTM D412 require?

At least 16 hours after vulcanization, then at least 3 hours at 23 ± 2 °C before testing; 50 ± 5 % RH conditioning for at least 24 hours only for humidity-sensitive compounds. Other temperatures follow ASTM D1349.

What grips are used for ASTM D412?

Self-tightening grips that hold the tab without slipping as it thins: pneumatic grips with rubber-faced or lightly serrated jaws, eccentric roller grips, or wedge grips for straight strips, aligned so the specimen is loaded along its axis.

How is tensile set measured in ASTM D412?

Stretch the specimen at 500 mm/min to the specified elongation, hold 10 minutes, release, recover 10 minutes, then measure the bench-mark distance; set is the percentage increase over the original. Set after break uses the rejoined halves of a ruptured specimen 10 minutes after the test.

What is the difference between ASTM D412 and ISO 37?

Both stretch dumbbells at 500 mm/min on 2.0 mm sheet, and ISO 37 Type 1 is close to Die C, but the die tolerances, specimen types and reporting differ, so results are not formally interchangeable. DIN 53504 S1 is the German equivalent of Die C.

Need a fixture, grips or a complete system for ASTM D412? Contact Universal Grip with your specimen details, capacity and machine connection and we will quote the right setup.

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