I was installing my strut brace that I just bought and managed to snap a bolt (see picture). How do I go about replacing the bolt?

 

You would need to take the strut tube out and buy a new hat.

 

You could probably get a new stud pressed on, but yes it's probably easier to replace the whole strut top. The bushing around the strut nut looks pretty cracked anyway.

Also, IMO that strut brace is a pretty poor design as it just ties together the front studs of the two strut tops, rather than spreading the load evenly across the tops of the strut towers. This may creating shearing forces that could damage the studs or warp the strut tops. These strut tower tops are pretty flimsy and can distort easily. I've seen people have to hammer them flat before because they have domed upwards over the years. Mazda must have recognised this too because on 84-84 models they incorporated ripple strips into the strut tower tops. Even with the ripple strips, my 85 model left strut tower has domed upwards a bit such that the studs fan out rather than run parallel.

 

That strut mount was about to blow, anyway - look at the stress crack around the perimeter. Replace both sides when you do this, as they're both in about the same shape, most likely. Also, those should only be torqued to about 40-60ft/lbs and you probably overdid it on the torque.

 

Thanks for all the advice and observations.

Actually, I was using a torque wrench set to 40lbs, lol. I'll replace both hats. Sounds like I should use the 84-85 parts, assuming that they fit.

I need new struts in the front anyway. I'm running tokico blues that just don't seem to stand up to the racing beat springs that I have. I'd love to get a set of Illuminas, but those just aren't around anymore.

Any suggestions on what to go with for shocks?

 

Just a side note, that is an RE-Speed strut brace.

 

My 2 cents... agree both strut mounts should be replaced due to age and aforementioned damage. The op is likely to have the same problem on installing replacements. Everyone seems to be overlooking the fact the stud snapped off from being waaay overtorqued. That's an 8x1.25 fastener and proper torque load should be no more than @25-28 ft lbs. max. Have not looked in fsm but certain the 40-60 ft lb. spec being quoted is for the strut shaft nut that tightens into middle of strut mount. Personally tighten the strut mount to body studs by hand with a medium length 3/8" ratchet,guesstimate 22-25 ft.lbs.
To be clear, KYPREO was referring to the added corrugations to the strut tower sheet metal for strength on 84-85 models. All Fb strut mounts are the same. Kyb#SM5304 is a good replacement strut mount,and is what came on car from the factory.
The Tokico Blue shock/strut & RB springs are a very common combo installed on 1st gens. Tokicos are very good quality,have had them on several 1st gens,most recently on my SE and consider the spring/shock combo to be a very good initial suspension upgrade.
Op doesn't state miles on car since install,may not know if installed by previous owner. There are other shock/spring options available.