Hi,
The OEM plugs are indexed, they do require it. But, also, be sure to torque the properly as well. This determines the depth of the electrodes into the combustion chamber as well as proper sealing in the head for proper compression.
The critical thing to remember is that there is NO Universal Standard on heat ranges. One Plug's manufacturer's '7' range plug can be completely different than another manufacturer's. Also, the Thread pitch and number of threads are critical. The OEM plug is designed to present the plug in the Combustion Chamber in the proper orientation and proper depth based on these, but only when properly torqued, another manufacturer's plug isn't...
Happy Motoring!... Jim'99
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