ASTM D638 is the standard test method for the tensile properties of plastics, and it defines five specimen types (I through V). In practice, two of them — Type I and Type IV — account for most of what labs actually order. Here's how to tell which one your test calls for.
Type I is the standard specimen for rigid and semi-rigid plastics when the material is thick enough (generally 7 mm or under in thickness, but substantial enough to machine or die-cut cleanly). If your method just references "D638" without specifying a type, Type I is usually the intended default. It's a larger dumbbell with a generous grip area, which makes it easy to hold in standard tensile grips.
Type IV was designed for use when you want to compare materials of different rigidities (for example, comparing a rigid plastic to a semi-rigid one), and it's also the go-to for thinner sheet. Its narrower profile concentrates the stress in the gauge section, which helps ensure the break happens where it should. Type IV is extremely common because it fits well on standard universal test machines and works across a wide range of materials.
Type II is a fallback when a Type I specimen won't break in the narrow section. Type III is for thicker specimens (up to 14 mm). Type V is a small specimen for very limited material or thin sheet. We can cut all five — but Types I and IV cover the large majority of real-world testing.
For most plastic tensile work, you'll land on Type I or Type IV, and thickness is usually the deciding factor. Our D638 dies are built to high tolerance with ground-edge blades so your specimens hold true geometry and your data stays clean. See our D638 dies →
D412, D638, D624 & 100s of other styles in stock at $225 each, shipped nationwide. Not sure which? Try our die selector.
