One of the threads on my FSA stem stripped out. The part that mounts the steertube.. the top one is fine and seems to hold the stem straight. Held the front wheel with my knees and gave the bars some tension in both directions, seems to hold fine. Gonna go to HD and see if I can find a longer bolt that will catch the threads that didn't get stripped. If not, do you think it'll be ok or should I start looking for a new stem? I have been eyeing the Nitto UI-75, might be my reason to buy it now .. lol

I would not want to rely on a single bolt clamping the steerer. I see three methods to fix it:

1. Buy a longer bolt of the same diameter and a matching nut. Thread the bolt all the way through and add the nut to the exposed end. An "acorn" nut would be best to protect your legs from any exposed threads.

2. Drill and tap the damaged hole to the next size up. Assuming the stock bolt is an M5x.8 you would have to drill and tap it to M6x1.0.

3. Buy a new stem and use a torque wrench when you install it so the same thing doesn't happen again.

If it was mine, I'd be shopping for a new stem or using one of the repair methods HillRider mentioned. (You might be able to add a helicoil insert to the list of possible repair methods.) If a stem fails, there's a pretty good chance of losing control and crashing. Even if you can find a longer bolt that'll engage whatever threads are left, who knows how strong it'll hold?

Another alternative for repair, if your stem holes are not drilled/tapped through, is to extend the hole through and use a longer bolt through the new threads. But for something as safety-critical as the stem I would be getting a new one ASAP, unless you were to repair it (I would do both bolt holes) with a Helicoil as SkyDog75 suggests, which will leave you with stronger threads than the original. Having your bar come loose in your hands is only funny in the cartoons. Whichever you choose, grease the threads and use a torque wrench so this doesn't reoccur. The bolts do not need to be anywhere near the stripping point to hold the stem securely.

It would be impossible to helicoil, even if you could find a metric set, not enough metal there for that, and the process would
cost more than a high zoot stem replacement anyway. Even redrilling to 6x1.0M is marginal for the amount of metal most
stems have. If a longer bolt doesn't work, get a new stem. I also endorse using a torque wrench.

I stripped the stem on my travel bike last summer. Even though it's a four-bolt stem, there's only half the gripping surface when one bolt strips. I was able to find a similar stem, and then I went ahead and bought a calibrated single-torque wrench to tighten the sucker. The wrench was cheaper than another stem.

Stems are cheap... faces are not.

Get a new or good used stem.
a good used one may be nearly the same cost as a bolt and locking nut.

I purchased a low torque precision torque wrench after stripping a stem bolt. The torque values are so low that stripping is always a danger. The torque values are too low for a Harbor Freight or similar torque wrench - around 5% of full scale --> the actual torque value in that range will around ±100% of the value, because the accuracy of the wrench is around ±5% of full scale (range).

Definitely would not ride a bike with stripped stem bolt, as noted above NOT safe.

i mean, stripped bolt for the steerer clamp....... i think the most likely accident is you hit a bump and suddenly you're bike is turning a hard left and you can't figure out why cos youre steering straight. happened to me once just from loose bolts. i think its very unlikely that you and your bars would go flying off your bike together. you can put a ton of pressure on your bars when the stem isn't even clamped down and its not gonna just snap off.

of course this is said from a point of view of desperation. if you can get to a bike shop and buy a new stem or fix it somehow tomorrow, or ride a secondary bike for a while, i'd opt to do that.

it might be an easy fix with a few nuts and bolts at the hardware store - but beware, they don't tend to have much fine thread stuff like most bolts on bikes. and i doubt they'd have anything smaller than what you already had to fit thru the hole. i'd sooner opt to go to a bike shop with used parts bins and try to find nuts and bolts there.

Yes, we knew the stripped bolt hole was for the steerer clamp, not the handlebar clamp. It's still not a good idea to use it with only one bolt holding.

As to "fine thread bolts", M5x0.8 is a very common metric standard and most hardware and home stores carry a good selection of metric bolts these days and that size is certainly readily available.

The OP does not have to find a smaller diameter bolt as a replacement. A longer M5x0.8 bolt can be threaded through the damaged area and allowed to project out the other end and then nutted. A larger size bolt (M6x1.0 is the next size up) could be used by drilling and retapping the damaged threads.

If you go to a bigger bolt, the bolt head may not fit the recess milled into the stem for the original bolts. I like using a longer bolt and a nylock nut. Get good quality bolts, I go to NAPA for this stuff. Repair will be as strong and prob stronger than the original. Now you will need a wrench for the nut in your bike tool kit.