When putting on my new rack (topeak explorer), the bolt that came with it is too short (longer than the fender one at least). Well actually that's my question, its just long enough to get a couple threads in with the 2 fender eyelets and the rack mount sandwiched in. Shouldn't it be long enough to utilize all threads or at least most for durability reasons? I feel like its going to pull out or snap off come time to load it up with all the gear.. or maybe I'm just doing it wrong

Get a longer bolt at a hardware store.

The manufacturer wasn't expecting you to use their bolt for fenders and a rack. Get a longer bolt from your LBS or from Ace Hardware (They are the only national chain I'm aware of that carries metric stainless steel socket head screws). Try to get as close to flush with the inside of your dropout.

still seems odd the manufacturer didn't make it longer.. anyone else have this issue? easy enough to go get new ones i guess, thanks.

Too long and it can rub the chain when in the highest gear.

use zip ties

It should use all the threads, and if there's enough sticking out to put a nut and washer on the other side so much the better. If it does protrude through the eyelet, though, there's a chance that the chain will catch on the bolt (or the nut) when you're in your highest gear, just like rogerstg said.

Lots of hardware stores have metric fasteners, or you could try an auto parts store.

I run into this problem when I use a cassette with a 12 tooth smallest cog (highest gear); with an 11 tooth the chain clears the bolt just fine.

This issue is very common. With various combinations of racks, fenders, and eyelets, the length of the bold may vary significantly. If your bolt is too short, you don't get good hold. If your bolt is too long, you get issues with the bolt rubbing the chain or even cogs.

It's a good idea to order a series of metric bolts to have around your bike supplies. You will find that you use them for many small tasks, e.g. fenders, racks, replacing the cheap rusting steel bolts with stainless steel on your winter commuter, replacing a bolt that vibrates off a friend's water bottle holder, etc. Having a little collection of various lengths of bolts is very useful for these situations.

I ordered a little collection from Bolt Depot and have found it very useful to have little stash.

https://www.boltdepot.com/product.asp...&cm=19&cd=1316

Peter White also sells them and has a little description of how to order them.

https://www.peterwhitecycles.com/hardware.asp

It is normal--they can't have a bolt that will fit all the possible rack fender combinations

5x .8mm machine screw most likely..

I like to have a couple of threads protruding on the inside of the eyelet, as long as it doesnt interfere with the chain. Also make sure you use a washer under the bolt.
Just get some stainless steel 5mm allen bolts of the correct size.

Note that 5mm bolts, the size commonly used for accessory attachments on bikes (racks, water bottles, etc.) are generally interchangeable with SAE ("American" or "standard") size of 10-32. Your local hardware store is probably likely to have a wider variety of stainless bolts in 10-32. I prefer to use bolts with Phillips heads when possible over hex heads, as I've found over the years that the hex heads in some types of 5mm bolts can be easy to strip out. I got a box of stainless ones from my local small hardware store for something like 10 cents per bolt, whereas the metric ones were 5x the price.

To mount your rack/fenders on the cassette side of the rear dropout, I suggest removing the rear wheel, attaching the rack with a bolt that is long enough to engage all the threads, and then cut off any extra length of the bolt that protrudes beyond the eyelet. You can easily use a hacksaw (careful not to scratch the paint!), or mark the cut-off length, remove the bolt, and cut it to size using a tool like an electrician's crimper/stripper tool that has pre-threaded slots that make it easy to cut bolts to length (that's what I usually use). Throw some blu Loc-Tite on the bolt, too, to keep it from coming loose.

if you own more than one bike you'll eventually acquire a stash of different 5mm hex head screws that can fit into a nice little plastic divider box.

They sell stainless steel metric allen wrench bolts at my local Ace hardware store. I have a stash in my shop. It's good to have several lengths. You want one that uses all the threads in the hole, but which doesn't protrude out the end far enough to cause any problems. I also replace all my rustable steel bolts with stainless.

It would be nice if they included the perfect hardware with each accessory you buy, but it's so easy and cheap to have your own stash I don't worry about it. It makes me feel prepared. (I have a stash of tubes, cables, cable housings, ferrules, and those little things you crimp on the ends of cables too. I'm almost like my own bike shop!)

I would not recommend attaching the fender stays using the same bolts as the rack. This requires a longer bolt and makes for a less sturdy attachment of the rack. I use a P clamp mounted to the leg of the rack to attach the fender stays.

Sorry, but I gotta say in my 35 years of working with hand tools and fasteners I've NEVER encountered anyone with an opinion like this. You're really suggesting that the six-sided positive engagement of a Hex Head Cap Screw is more likely to strip than the shallow, sloping edges of a Phillips head? A Torx drive fastener is sort of Phillips like and works a lot better, but I've tried to replace every Phillips head screw in my life with hex heads if it can be done. Phillips is only good for holding covers on the back of electronics cases, where no torque is needed to fasten it appropriately. In my opinion, of course.

You may be right, but it is hard enough to line up the rack, fender stays and eyelet; and start the bolt without cross threading the eyelet using the correct bolt. I wouldn't take a chance on using anything but a metric threaded bolt. I think that the metric size OD is just a hair smaller than SAE. While metric recess head steel capscrews are relatively easy to find, stainless steel are harder to come by. I've used the plain steel ones and with a little care they don't cause a problem. I grease the treads, rather than use locktite, and check them regularly for snugness; which is a good idea regardless of bolt matrial.

If you use the same bolts for both the rack and fender:

Rear - you want the rack to be next to the frame dropout, the fender outside of that. If you had the rack outside of the fender, that is weaker when your rack is not touching the frame mount.

Front - you can put the rack on the outside of the dropout and fender mounts inside of the dropout, in which case you need long bolts and nuts to attach the fenders. (I do not use disc brakes, not sure if this would work on such bikes.)

I also use blue locktite on all rack bolts.

Avoid the button type heads that use a 3mm allen wrench, the heads are not as strong as the bolts that use the larger heads. They work fine for a water bottle bracket but otherwise are too weak for a rack.

I carry a few extra bolts on my frame at all times. On my LHT, I use all brazeons, but for the rear rack mounts on the seat stays, I have a few extra bolts, washers and nuts threaded into the other side of the rack mounts.

I do this as well, including keeping a pair of SPD cleat bolts in one set of brazeons. I've only ever lost a cleat bolt once, but it was at a ridiculously inconvenient time and really caused me some problems.

That's not a bad idea, I've lost exactly one cleat bolt as well, and it did make my life a lot harder until I had it replaced. Only problem was mine fell out while riding, so I couldn't unclip. I had to reach down, loosen the strap to my shoe, and pull my foot out (kinda like a tri).

Yeah, in a pinch, but they won't last long. I had a cap screw shear off from a rack once and had to affect a road repair with a wire tie to stop the rattling, there was no load on the rack.

Someone mentioned ACE as a source for stainless metric cap screws; good to know, I've currently got some black steel screws from HD holding my rack and fenders in place, they're ugly and rusting.

Well, NoGaBiker, now you HAVE encountered someone with that opinion! :-) Perhaps I should clarify by saying that I prefer the Phillips interface to the easily stripped-out hex heads on the small "button" bolts that are often provided by bike shops (typical for water bottle cages, for example). If we're talking about socket-type bolts with more "meat" on the head, then I agree with you. Peter White also makes the distinction between cap and button bolts. See https://www.peterwhitecycles.com/hardware.asp