Hole size under seat?

I’m looking to mount the bracket and radio body of the ftm-400xdr to holes under the seat for a secure fit. What’s the size of the frame holes in the seats (thinking passenger side would work for my application):
https://bit.ly/3pl0wvl

(Trail Tacoma)


I’ve seen some other solutions like kydex and zip ties, but maybe there are some other, more elegant and economical ideas to mount a radio body (metal amp bracket?) any other thoughts welcome.

thanks!