What thread size is this firewall screw ?

[HECTOFL5TYPER]

Anyone know what size nut will fit this Firewall screw ? Trying to mount my Radium catchcan. It won’t fit with the Hondata Canflex. Thank you.

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[AZCWTypeR]

The coarse threads suggest it's self tapping, normally used with a plastic nut.
Otherwise check with a thread pitch gauge and calipers.