Hildebrand Hardness Testers and Durometers

Q: What is the difference between Shore A, Shore D, and Shore OO durometer scales?

All three scales comply with ASTM D2240 but use different spring forces and indenter tip geometries to match material stiffness: Shore OO uses a very light spring force (113 gf) and a spherical Ø 2.4 mm tip for ultra-soft foams, sponges, and gels. Shore A uses an 822 gf spring load and a blunt 35° frustum cone for normal soft-to-medium rubbers, elastomers, and soft PVC. Shore D uses a heavy 4,536 gf (10 lb) spring load and a sharp 30° cone for hard rubbers (above 90 Shore A) and rigid thermoplastics. When a specimen reads above 90 on the Shore A scale, ASTM D2240 recommends switching to a Shore D durometer; when a Shore D reading falls below 20, switch to Shore A.

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Industrial Hardness Testers & Durometers for Elastomers, Plastics, Textiles & Metals

ABQ Industrial offers a comprehensive range of portable and laboratory Hardness Testers and Durometers organized across seven specialized subcategories: Barcol Hardness Testers, Durometers, Durometer Test Stands, Textile Durometers, IRHD Hardness Testers, Metal Hardness Testers, and Durometer Accessories. Partnering with world-class manufacturers including Checkline, Rex Gauge, Bareiss, Imada, Asker, Hildebrand, DeFelsko, Barber-Colman, and InnovaTest, our instruments deliver NIST-traceable compliance with ASTM, ISO, DIN, and NFPA standards.

F.A.Q.

What is the difference between Shore A, Shore D, and Shore OO durometer scales?

All three scales comply with ASTM D2240 but use different spring forces and indenter tip geometries to match material stiffness:

Shore OO uses a very light spring force (113 gf) and a spherical Ø 2.4 mm tip for ultra-soft foams, sponges, and gels.
Shore A uses an 822 gf spring load and a blunt 35° frustum cone for normal soft-to-medium rubbers, elastomers, and soft PVC.
Shore D uses a heavy 4,536 gf (10 lb) spring load and a sharp 30° cone for hard rubbers (above 90 Shore A) and rigid thermoplastics. When a specimen reads above 90 on the Shore A scale, ASTM D2240 recommends switching to a Shore D durometer; when a Shore D reading falls below 20, switch to Shore A.

Why should I choose an IRHD or Type M tester instead of Shore A for O-rings and thin sheets?

Standard Shore A durometers require a minimum flat specimen thickness of 6 mm (0.24"); on thinner sheets or curved O-rings, the indenter force penetrates through the rubber and senses the hard support table underneath, producing artificially high readings. IRHD Micro Hardness Testers (per ASTM D1415 / ISO 48) and Type M O-Ring Systems (like the Rex OTK-DG paired with the Rex OS-3 Stand) use micro indenters and low forces specifically designed to test materials from 0.030" (0.76 mm) to 5 mm and curved O-ring cross-sections without destructive cutting.

Why is a durometer test stand recommended for ASTM D2240 compliance?

Hand-held durometer readings vary between operators due to differences in pressing force, approach speed, and angular tilt. Mounting your durometer on a constant-load or motorized stand from our Durometer Test Stands subcategory—such as the Imada YMS Motorized Stand, Imada SY Lever Stand, or Rex OS-2H Hydraulic Dampened Stand—applies the exact ASTM D2240 mass (1 kg for Type A/B/E/O, 5 kg for Type C/D/DO, or 400 g for Type OO/OOO) at a controlled descent rate and strictly perpendicular contact angle.

How do I verify durometer accuracy in the field or laboratory?

Per ASTM D2240, durometers should be checked regularly against certified reference blocks to verify spring calibration and indenter condition. ABQ Industrial supplies Rex Durometer Test Block Kits (TBKC Series) with NIST-traceable certificates, Checkline TBK-HP / HP-PT Test Blocks, Hildebrand IRHD Test Block Sets, and the Rex RDC-1 Durometer Calibrator for full in-house spring-force calibration.