Ask HN: Different size nuts?

Ask HN: Different size nuts?
2 by lsiunsuex | 0 comments on Hacker News.
I know HN is more computer / IT / programming related but you see the random article / question here and I've always seen people from different backgrounds post, so... There are usually some pretty smart people here. In replacing spark plugs last night on a 2016 Ford Mustang - I had to remove my strut tower brace to remove the engine cover to gain access to the spark plugs. The 2 bolts for the strut tower brace closest to the engine are 10mm by 1.25 thread pitch while the 2 farthest from the engine are 10mm by 1.5 thread pitch. (4 bolts on either side). I got the nuts confused - they weren't marked differently and I couldn't see the difference in pitch - so... I stripped 2 of the 1.25 nuts - 1 on either side. (I'm told I'm safe to drive it with 3 of the 4 properly torqued to 35lb until I can get a die to recut the bolts, and new nuts) The question - WHY would a designer / engineer use 2 different kind of bolts / nuts - so closely to each other, providing the same purpose? I'm curious what the reasoning is behind this. Do the different thread pitches provide different security for the bolt? With the amount of boost I'm running (tuned) and methanol injection - I'm told I should change the plugs every 10-15k miles so this won't be the first or last time the strut tower brace will need to come off.