To be honest, buy with a screw like that, if there's room on the back side, run a longer bolt and put a 3mm locknut on it. I just did that on my savage flux.
I usually buy nuts and bolts in 20/50 packs from mcmaster.com. They have a lot of black oxide bolts down to 3mm. I usually buy long and cut them off if I need to with a dremel or hand saw. I keep different kinds on hand.
button head 3mm 12,15,20mm in length
same with cap heads and flush mount.
I also keep some 4mm stuff on hand too.
You can buy nylock nuts, they seem to work best for RC as well as 3mm washers, small or fender type/larger ones to cover more surface. I usually buy enough to make the $10 shipping not be so bad. $100 every few years keeps me going. I've been buying pretty much all my nuts/bolts/washers from mcmaster.com for nearly 20 years for RC stuff. When you have 5+ RC trucks at any given time, you have to keep a lot of things on hand.
I have little containers I got from the container store many years ago to keep the bulk items in:
Anyway, back to your issue, I'd definitely go with a screw that is long enough to stick out the top side 2-3mm because if you don't have the screw loosen and fall out, if you hit something hard enough, it will snap off flush in your alloy steering arm. Then you have to hack at it with a dremel to get it out. If the screw came out the top a few mm, you could at least get some needle nose on it to get it out the top. Personally, with a part like that that allows room for a nut, I drill the threads out and use a nut only to keep the bolt in place. So, when it does snap the bolt off, it's not a pain to get it out.
Just my nickles worth.
😉
So I’m new. My apologies if this is a dumb/easy to answer question but;
