For elastomer jaw-coupling spiders, 92 Shore A (typically yellow) and 98 Shore A (typically red) are the two most commonly specified hardness grades, with 98A carrying roughly 20 to 30 percent more nominal torque per coupling size and 92A delivering measurably higher vibration damping and electrical isolation [S1][S2].
Both grades sit on the Shore A scale used for softer elastomers, are usually injection-molded thermoplastic polyurethane (TPU) rated for service from roughly -30 to +100 to +120 °C, and come color-coded by manufacturer to keep selection mistakes out of the stockroom [S1][S5]. They are not interchangeable: choosing the wrong grade is one of the leading causes of premature spider failure, vibration-related bearing wear, and unplanned downtime in servo, pump, and conveyor drives [S2].
Where 92A and 98A Sit on the Shore A Scale
Shore A is the durometer scale used for soft to medium elastomers; a blunt indenter is pressed into the specimen under a defined spring force and the penetration depth is converted to a number from 0 to 100, with higher numbers meaning a harder material [S2][S5]. Spider grades cluster at 80 ShA (soft, blue), 92 ShA (medium, yellow), 98 ShA (firm, red), and 64 to 65 ShD (rigid, green) once the elastomer is hard enough to push onto the Shore D scale used for rigid plastics [S1][S5].
On a typical jaw coupling, 92A and 98A together cover most general-purpose and hydraulic service; Lovejoy's NBR spiders, by contrast, sit at 80 ShA for best damping and 90 ShA for higher torque [S7]. Reading the spider as a polyurethane elastomer component rather than a generic rubber helps explain why two adjacent Shore A points behave so differently in service.
92A vs 98A: Side-by-Side Selection Criteria
The 92A spider is the lower-torsional-stiffness option of the pair: it twists further under the same load, which absorbs torsional shock and damps vibration, but it transmits less nominal torque per coupling size than 98A and runs at a slightly lower peak temperature [S1][S5]. Ringfeder's yellow 92 ShA and red 98 ShA inserts are described as the two "most common" grades precisely because together they balance damping, torque transmission, and operational temperature for typical servo, positioning, and main-spindle drives [S1].
By comparison, R+W's standard TPU insert (type A) at 98 ShA covers 2 to 20,000 Nm across -30 to +100 °C, while their softest 80 ShA type C is capped at 2 to 400 Nm and -20 to +80 °C, with a much larger twist angle under load [S5]. A direct four-criterion comparison for the two grades most engineers are choosing between:
1. 2. Vibration damping: 92A better, larger angle of twist under load [S1][S5]. 3. Peak continuous service temperature: both TPU grades cluster near 100 to 120 °C; 98A tolerates slightly more heat build-up from higher torque, 92A is preferred where ambient is already high [S5]. 4. Electrical isolation between driving and driven shafts: both are isolating, with 92A and 98A standard TPU both serving as the dielectric layer in a jaw coupling assembly [S1][S2].
Which Drive Should Use 92A, and Which Should Use 98A
92 ShA is the default for general-purpose and hydraulic applications where vibration isolation and electrical isolation matter more than peak torque: packaging machinery, conveyor lines, encoder drives, and positioning drives with moderate inertia mismatches, plus any drive where the driven shaft is a sensitive instrument [S1][S2][S8]. Timken's CJ-series metric curved-jaw spiders explicitly call 92 ShA (yellow) the general/hydraulic grade, sitting below a 98 ShA (red) option for higher torque loads on the same hub [S8].
98 ShA is the right pick when the coupling must transmit higher torque per size, when ambient temperature is mid-range, or when the drive has low vibration but high continuous load, including main spindle drives, machine-tool spindles, and high-power servo-to-ball-screw pairs on servo motors sized close to the coupling's nominal rating [S1]. Where the load profile is more aggressive still, manufacturers step up to 64 to 65 ShD (green) hytrel or reinforced TPU inserts, with the 64 ShD-H hytrel grade transmitting the highest torque and covering the widest temperature range of the five standard colors [S1][S5].
Limits, Failure Modes, and What the Shore Number Does Not Tell You
A Shore A number is a single-point indentation reading at one temperature, on one specimen, in one lab, so it is a useful ranking tool but not a life predictor. KTR's own technical note reminds engineers to record test duration and temperature with the reading, because rubber resilience means the same spider can read several points harder in a cold cell than in a warm one [S2]. Common failure modes for mis-selected spiders are predictable: a 92A grade pushed into high-torque service overheats, hardens further, and cracks at the tooth roots; a 98A grade used in a high-vibration drive stays cool but transmits shock into the driven bearings.
For a hardness-vs-performance map of a specific product line, see the elastomer coupling inserts guide entry on how TPU, hytrel, and NBR behave across the Shore scales. Where the application is fundamentally about controlled slip rather than elastic torque transmission, a fluid coupling or a coupling clutch belongs in the conversation instead, and a Shore number stops being the right question at all.
Procurement and Field-Check Checklist
Specifying a 92A or 98A spider should always cite three things on the purchase order: the Shore A value, the elastomer family (TPU, hytrel, or NBR), and the color code used by the chosen hub family, because color is the only field-readable proxy for hardness once the spider is out of the bag [S1][S8]. On existing equipment, Miki Pulley's ALS-B aluminum split spider at 97 ShA is a good reminder that not every supplier lands on 92 or 98: mid-grades such as 95 or 97 ShA exist for OEMs who want a torsionally stiffer feel than 92A without jumping all the way to 98A or to 64 ShD [S9].
For mixed-drive plants running both hydraulic and servo lines, the practical rule is: specify 98A on the high-torque servo and spindle side where heat build-up is acceptable, specify 92A on conveyor, pump, and instrument drives, and reserve 80 ShA blue and 64 to 65 ShD green for genuinely soft or genuinely rigid cases rather than using them as compromise grades [S1][S5][S7].
Trackable signals to watch over the next planning cycle: any 2026-line TPE datasheet updates that re-state 92A and 98A torque derating above 80 °C, and Lovejoy's 90 ShA NBR grade continuing to show up as the outlier choice on retrofit hydraulic-pump frames [S7][S10]. A useful adjacent reference for the way a single hardness choice cascades into a whole disc coupling or jaw-coupling service interval sits in the spec library as well.
Related analysis: Pit Depth vs Lip Length: Spec Map for Recessed Dock Leveler Installation.