micwells

What should have been a simple problem has me really confused. I was riding and I noticed my rack screw had popped out and the rod got caught in the gears on the rear wheel. I went to remove the other screw so i could get a match and realized the threads don't actually fit the hole but slide in and out. So I went to a bike shop to get a replacement, and found that there are 2 types of screw for the back wheel holder. There is a size for a more expensive bike, and another for schwinn types. The shop owner gave me screws that were too big, when i went back he didnt have other sizes. I then went to another shop and he coouldn't help either. Although I suspect if I brought my bike in they could fix it in a second. I then tried to match the size at a hardware store and those were also too big. Does anyone know how I can get 2 screws that will fit these holes? Since the back rack also acted as a mud guard, if I don't find some, I'm screwed. :-)

LesterOfPuppets

I've had bikes with 5mm, 6mm, and some SAE size. I'm guessing you're looking for the SAE bolts, so you'll have to check into a place that has a good SAE selection, probably #12 bolts.

I've drilled out SAE rack bolt holes to 6mm and used M6 bolts with nylock nuts.

dsbrantjr

I refurbed an old Schwinn Collegiate which used M6x1.0 rack/fender bolts.

techsensei

I always just use a standard M5 bolt and nut (the "more expensive bike" size) to secure racks to bikes that have larger sized eyelets, because if you get the correct size, the bolt won't fit through the hole in the rack.

micwells

I have since tried screw from a newer schwinn bike - and it was too small, then I tried the bolts from the bottle holder of the same bike and they were also too small - those i believe are 7.6mm so the ones i need are bigger than that? The bike model is diamondback parkway - I am not sure of the year.

Bill Kapaun

What are you measuring to get 7.6mm? The screw head?

Don't you have a local store that specializes in threaded fasteners?
Take the screw in and let them you their thread gauge.
Even I have a thread gauge. I can't believe your LBS doesn't.

You can just use a high strength bolt & nut. Best solution if the hole isn't threaded or threads are damaged.
You'll want the theaded end to point out, so it doesn't interfere with any rotating/moving parts.
Probably the best, considering your skill level.

Personally, I would drill it out to the next larger size and thread it with the appropriate tap.

Some of your terminology is confusing.
"Back wheel holder"?

Pictures could be very useful!

HillRider

Most rack and nearly all water bolts cage bolts are M5x0.8 mm. That is the bolt diameter is 5 mm and the thread pitch is 0.8 mm between adjacent threads. It is a very common size. The other size sometimes used for racks is M6x1.0 and once in a while an SAE #10-32 .

There is no "7.6 mm bolt" unless you measured a 5/16" SAE bolt and no bike uses them for anything or are you measuring the length?

Andrew R Stewart 

Maybe I'm missing some detail (and it wouldn't be the first time) but do we even know the model or year of the Schwinn bike? Remember Schwinn has had domestic mass volume and limited production years ago and Asian production since. The rack eyelets (on the drop outs) and the seat stay (brake bridge) mounts have been different during the 45 years of my experience with Schwinns.

Also we don't know if the eyelets are even threaded. Or what size bolt hole the rack braces have. So how do we advise the OP with specifics? Of course the Op hit the nail on the head, bring the bike to the LBS. Andy.

LesterOfPuppets

Those bolts you tried were probably M5. I'd try out M6 next, if you can get a couple from a hardware store. I have the feeling the bike shop only tried M5 and the standard SAE rackmount standard, from your description of the scene.

cny-bikeman

Almost all chain hardware stores have both SAE and metric bolts in a large enough variety that one of the threadings will fit - if the holes are indeed threaded.