The 6987 is a ZFR6F-11G plug. plugs are pre-gapped to 0.043"

I think the code breaks down as:
Z - extended projection
F - 14mm diameter x 1.25mm thread pitch, 19mm long threads (3/4" = 19.05mm), 16mm hex (5/8" = 15.875mm)
R - Resistor plug
6 - Heat range 6. Seems to be good for street engines. For race engines I usually use a colder 8 heat range spark plug.
F - Firing end construction, I think "F" is a code for how far the projected tip is, but I don't see it listed in the chart?
11 - Pre-set plug gap 1.1mm = 0.043" (0.433071")
G - I think this is Copper core Ground Electrode?