those grommets are for the tail light, but they're the same size if memory serves.
You'll also need a grommet for the wire harness if the wire harness is still there. The grommet for the taillight's wire harness appears the same size, but the signal light's wire harness is thicker, has more wires. Think I bought a grommet from the hardware store or had a grommet in a package of miscellaneous parts from eBay. Good news is the grommet is generic for electronic equipment (right pic). They're just to protect the wires from the sharp edges of the round cutout, not as a cushion for a bolted rubber mount (bottom pic, middle grommet).


