how to find a thread size.

I want to find the bolt size I need how do I do that?
Situation I have a 22 Tacoma access cab with the utility delete. I want to mount ham radios behind the black Plaistc cover in the access cab where the seats would mount if they were there.
is there a resources to find the thread size or a way to determine tone bolt size needed with out messing up the treads

 

i use a set like this

$27 LOZAGU 44pc Nut and Bolt Gauge Set - 44 Gauges 23" & 21 Metric, Male/Female, Bolt Size & Thread Checker

https://www.amazon.com/gp/product/B0CD7G5KVG?ie=UTF8

but i'm regretting it(having to haul an entire 'anal bead' set everywhere to check a single thread is a PAIN), i'd suggest a set like this that you can more easily check them individually.

Nut and Bolt Thread Checker - 26PCS(14" & 12 Metric) Identifier Gauge Set Individually Assembled Bolt Sizing Gauges Perfectly Suitable for Size Check Free Detecting Compact Thread Checker Box

https://www.amazon.com/Nut-Bolt-Thread-Checker-Individually/dp/B0CGLJJL6Q?crid=39OAB50EE9BTN&keywords=thread+checker+string&qid=1702843580&sprefix=thread+cheacker+string%2Caps%2C204&sr=8-34