ASTM D2000 places silicone rubber on the high-temperature end of its Type table, with FE pegged to a 200°C test and GE pegged to 225°C, while both sit in E-class for oil-swell resistance, which is the reason the callout string is widely used for VMQ sealing compounds [S2][S3].
The "FE" and "GE" pair is specific to the elastomer community: F and G are the Type letters that map to the heat-aging test temperature, and E is the oil-swell Class letter; together they tell a buyer the compound is a high-temperature silicone with limited oil resistance, not a nitrile or FKM substitute [S2][S4].
Anatomy of a D2000 Callout: Where FE/GE Sit in the String
A D2000 line callout is a four-block string: document prefix, grade, type/class plus hardness plus tensile, then optional suffix callouts [S2][S3]. The full example published by Jehbco, "ASTM D2000 M5 GE 706 A19 B37 EO16 Z1", decodes as: M (SI units), grade 5, type G (225°C), class E (oil swell limit), 70 ±5 Shore A, 6 MPa minimum tensile, then the suffix block A19, B37, EO16, plus a user-defined Z1 [S3].
The "M" prefix changes the unit system: with M, the tensile digit is read in MPa (multiplied by 145 to convert to psi); without M, the same digit is read in psi (divided by 145 for MPa) [S4][S6]. The grade number (1–9) is not a quality score, it is a count of how many additional suffix requirements must be added to the basic material, so grade 5 means five suffixes in the callout string [S2][S3].
Type and Class Tables: Why F and G, Why E
Type letters A through K in D2000 are not material codes, they are heat-aging test temperature codes. A=70°C, B=100°C, C=125°C, D=150°C, E=175°C, F=200°C, G=225°C, H=250°C, J=275°C, K=300°C, as published in the Warco reference Table A [S2]. That is why "F" places a compound in the 200°C test bracket and "G" places it in the 225°C bracket; this is the most common way silicone compounds land on the upper end of the type scale.
Class letters define oil swell after 70 hours in IRM 903 oil, and the table runs A through K with progressively tighter volume-swell limits [S2][S4]. "E" sits in the upper half of the swell range, which for silicone (VMQ) is essentially the realistic band: VMQ swells significantly in petroleum oil, so a tight A or B class is normally unattainable, and the standard is satisfied by reporting the actual swell at E-class limits [S3][S7]. Elastoproxy summarises the point: "Type and Class are the most important callouts to consider" because they map the polymer family to the heat-and-oil envelope [S7].
FC vs FE vs GE: Where Silicone Falls on the Heat/Oil Trade
Jehbco's worked examples show three distinct silicone envelopes under D2000: M2 FC 709 is a hard, high-tear silicone (Shore A 70 ±5, 9 MPa minimum tensile, F-type 200°C, C-class oil swell), and M3 GE 310 A12 is a soft, high-temperature silicone (Shore A 30 ±5, 10 MPa tensile, G-type 225°C, E-class oil swell) [S3]. The contrast illustrates the rule: the Type letter steps the test temperature, the Class letter steps the oil-swell tolerance, and digits 1 and 2 (after the type-class pair) set hardness then tensile.
A practical comparison: FC vs FE vs GE on three engineering axes. Heat-aging test temperature: FC=200°C, FE=200°C, GE=225°C (FC and FE share the F-type test but differ in C- vs E-class oil-swell tolerance). Oil-swell class (lower letter = tighter): FC is C (tighter), FE is E (looser), GE is E (looser). Typical silicone use-case bias: FC tends toward high-tear mechanical silicones, FE toward general-purpose high-temperature sealing, GE toward soft, very-high-temperature static seals [S2][S3]. Selecting between them is therefore not about quality, it is about which combination of heat and oil envelope the part will see.
Decoding the Hardness and Tensile Digits
After the Type/Class letters, the next digit is the nominal Shore A hardness with a standard ±5 tolerance for basic callouts, and the digit after that is the minimum tensile strength [S2][S3]. Apple Rubber's worked example uses 7 for 70 ±5 Shore A and 14 for 14 MPa tensile, with the same MPa reading applying to any M-prefixed callout [S4]. Without the M, the 14 would be read as 14 × 100 psi = 1400 psi minimum tensile [S4].
The two digits operate as a paired selector: a 706 callout specifies 70 ±5 Shore A and 6 MPa minimum, a 310 callout specifies 30 ±5 Shore A and 10 MPa minimum [S3]. For silicone, hardness below 30 Shore A is unusual because tear strength drops fast and the compound becomes difficult to mold; above 80 Shore A the elastomer loses much of silicone's flexibility advantage and approaches a rigid gum, so the practical window for VMQ under FE and GE callouts sits in the 40–70 Shore A range in most converter datasheets.
Suffix Callouts That Tighten a Silicone Specification
The suffix block is where most of the engineering work is encoded. Suffix letters map to test categories per Jehbco's Table 2: A = heat resistance, B = compression set, C = ozone or weather resistance, D = compression-deflection, EA = aqueous fluid resistance, EO = petroleum fluid resistance, F = low temperature, G = tear, H = flex, J = abrasion, K = adhesion, M = flammability, N = impact, P = staining, R = resilience, Z = any user-defined special requirement [S3]. Each suffix is followed by two digits: the first is the test method or condition, the second is the test temperature [S2][S3].
For an FE or GE silicone seal, three suffix patterns dominate. A19 is the most common heat-age addition: heat-age for 70 hours at the test temperature indicated by the second digit (1=..., 9=225°C in some tables) and verify tensile and elongation change limits [S3]. B37 is the standard compression-set callout at a specific test temperature for 22 or 70 hours; this is critical for static seals because silicone's compression-set recovery is one of its weaker properties relative to nitrile or EPDM. EO16 specifies petroleum-oil immersion for 70 hours at the indicated test temperature; for FE/GE this is the callout that documents silicone's known oil-swell behaviour rather than hiding it.
FE/GE Callouts in Real Spec Use
Apple Rubber notes that D2000 was framed by SAE and ASTM for automotive, but is in practice used across medical, aerospace, and industrial sealing because it is the only widely adopted classification that decouples the polymer family from the physical-property envelope [S4]. This is exactly the use case for FE/GE silicone: a buyer who needs a 200°C or 225°C-rated soft elastomer with documented oil-swell behaviour can write the callout and have multiple compounders bid to the same line.
For gaskets, O-rings, and static seals in food-grade, medical, and high-temperature industrial service, the practical baseline callout is something like M2 GE 505 A19 B37 EO16 (50 ±5 Shore A, 5 MPa tensile, heat-aged at the G-type temperature, compression-set tested, oil-swell documented) [S3][S7]. For softer dynamic seals, M3 GE 310 A19 is the typical starting point, with a F19 low-temperature suffix added if the part must seal at –55°C or below [S3]. For hard, high-tear parts like diaphragms, the FC family is preferred over FE/GE because tear (suffix G) rather than heat is the controlling property [S3].
Limits, Failure Modes, and Cross-Standard Linkage
D2000 is a property specification, not a recipe specification: the callout constrains tensile, hardness, heat-age, and swell, but does not dictate polymer, filler, or cure system [S8]. This means two FE callouts from different compounders can deliver different compression-set behaviour, different post-cure levels, and different fluid compatibility profiles, all while passing the same line callout. Engineers writing an FE or GE specification for a safety-relevant seal should pin the critical suffix values and add a Z-callout for any property the standard does not cover.
The polymer-family side is governed separately by ASTM D1418, which assigns VMQ to silicone rubber, FKM to fluoroelastomers, and so on; D2000 and D1418 are designed to be used together, with D1418 naming the polymer and D2000 naming the property envelope [S8]. For VMQ specifically, FE and GE are the workhorse D2000 envelopes, and the boundary between them is simply the 200°C vs 225°C heat-aging test point; the practical upper continuous service temperature for VMQ compounds in either envelope is in the +200°C to +225°C range referenced for FE/GE silicone, with excursions to higher temperatures limited by compression-set recovery rather than tensile loss [S3].
Specifying a VMQ compound under FE or GE will not automatically deliver low-temperature flexibility; that property is added with an F-suffix, and the underlying polymer choice (e.g. phenyl-containing VMQ grades) is what really extends the low-temperature floor. For fluorosilicone alternatives under similar heat envelopes, D1418 FVMQ and the related FKM families are outside the FE/GE space and use a different Type/Class position. Related reference material on the ASTM D1418 FKM type 1 dipolymer composition and cure and the VMQ spec boundaries for high-consistency silicone gives the polymer-side context to pair with the FE/GE property envelope here. For background on the broader silicone-rubber material family covered by these callouts, the silicone rubber entry and the industrial rubber entry give the family-level property ranges.
Trackable signals: any compound re-classification under a future ASTM D2000 revision (the standard is on a multi-year update cycle, and any change to the Type/Class table would shift where FE and GE sit), and any compound-side shift from E-class to a tighter D-class as VMQ filler technology improves oil resistance.
For component-level specifications, see construction machinery and equipment.