Exact bolt size for rear seat to add space for sub

I have wasted money on m10x1.25x40 and m10x1.5x40 bolts trying to place more washers than the oem can hold in order to fit my sub from mr marv and I’m getting irritated. I’ve read the m10 part but the threads aren’t working with what I’ve bought. Thanks in advance to anybody who’s done this

 

Take the OEM bolt to your hardware store and use their thread gage to figure out exactly what you need.

 

Sorry to digress but how much lift do you require for this mod?

 

I’m needing to fit another 1/2 inch of washers onto the bolt to move the seat up another 1/2”. I’ve already got 3/4” spacers but it’s not enough

 

I’ve done that. Lowe’s nor fastenal had them. Dealer has them but they’re same length as what I’ve got. I know that ppl have done this on here. I remember reading the threads about it but I can’t find the post anywhere