While Lovejoy's straight jaw coupling is robust, ubiquitous and economical... is is also fail safe & requires no grease/maintenance free. (Fail safe means that if and when the elastomeric spider fails, torque will continued to be transmitted as the jaws of the two hubs interlock directly. Requiring no grease means both greatly reduced environmental leakage risk, which may not be true for grid or gear couplings, and no periodic re-greasing required.)
While being fail safe is great in some applications, is not desirable or valuable for all applications. Additionally, the traditional jaw coupling requires that at least one of the two hubs to be pulled back to replace the elastomeric spider. (Note: There is a fail-safe Snap Wrap version that enables spiders to be radially replaced without moving the hub for lower speed applications.)
The Jaw In-Shear Coupling (pictured right) is a straight forward 4 piece non-fail safe design (meaning the coupling will no longer transmit torque if/after the elastomeric element fails) that is optimized for quick elastomeric element replacement (with neither jaw coupling hub being required to be moved).
Because the coupling is non-fail safe, the coupling behaves similar to a non-calibrated fuse to prevent equipment damage in the event of torque overloads. (Note: Elastomers are not rated or designed to fail at a specific torque level, so other methods such as rated shear pins or torque limiters should be used if a true fuse is required.) Instead of the spider being compressed between interlocked jaws of each coupling hub (a traditional jaw coupling configuration), the Jaw In-Shear coupling has the hubs drawn apart with jaws aligned axially. The wide spider is thus in a shear-plane.
Jaw In-Shear elastomeric spiders, being radially removable, results in saved maintenance time and money. The coupling's retaining ring encloses and secures the In-Shear Spider, using an intuitive twist-lock design that will not work loose and requires no fasteners. Furthermore, the Jaw In-Shear uses Lovejoy's industry-standard L-Type and C-Type jaw coupling hubs which are both cost effective, and quite possibly already installed on the equipment (meaning a retrofit cost will be reduced to the Jaw In-Shear elastomeric spider and retaining ring. The Jaw In-Shear spider is made from a tough Urethane formula offering high durability, chemical resistance, temperature range, and torsional softness. Jaw In-Shear coupling designs are available for jaw coupling hubs with max bores up to 9.0 inches (229 mm) and 183,333 in-lbs (20,714 Nm).
Recommended Follow-On Reading: For a full review of jaw couplings, and additional commentary on Jaw In-Shear couplings, please read: Jaw Coupling Overview - Features & Benefits, Design Basics, and Element Options