Taking the rear controls arms of a 90 miata and the upper bolts are 9mm dia while the holes in the arms and the bushings are 10 mm. Is that normal or did someone put undersized bolts in? The bolts look to be in good shape (not beat up or worn) but I'm thinking that they didn't design 2mm of play in the suspension. If they are supposed to be 10 mm will go pick up a new set of bolts.

The lower ones have no play in them. In fact they were seized in the bushings. Haven't looked at the front ones yet.

They did change the bolts early on in the Miata lifecycle to a different design with a locking groove, I forget the specifics though. I remember changing all mine out on my 90 because the earliest ones tended to slip. I don't recall them changing diameter, however.

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2005 Forester XT (Daily/B2Tuned), 2000 Subaru Impreza 2.5RS P4WD Class Rally Car, 2006 WRX RallyCross Car (Sponsors: Rally-Tech, Great North Performance, ISI Automotive)
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The lower adjustable ones are 12mm, and do have the groove in them (have new ones coming for those). The collision guide lists the part numbers for the lower arm bolts but not the top ones. Google has been no help. Will call the dealer today and see what they say.

Mills Mazda one of our class sponsors are really helpful

Yep, Mills has been great. The bushings are coming from there.

Part number is 9978-01075 but they couldn't tell what size it was. Google says that part is a M10x75 bolt. That would explain a few things was feeling on the track.

BTW the last few digits seem to give the bolt size. The lower shock bolt was a 9978- 01270 (M12x70).