Need specific RD clamp bolt size and threads
 

I recently bought new shifter cables for my dad's '89 Schwinn World Sport and I had to take off the old, dry rotted ones to bring in to the LBS for sizing. But anyway, I took them off and threw front and rear derailleur clamp bolts off to the side and forgot about them. I found a front clamp bolt and I can shift the front perfectly! (I have never been able to do this on this bike before). But the rear derailleur, which is a Shimano SIS RD, has a threaded hole for the clamp bolt and I can't find the original bolt. Can someone tell me what the size and threads are for this clamp bolt? I will post more info if needed...

TIA,

Josh

Sometimes I feel like an analog guy who's trapped in a digital world. Here's what I would do:

First alternative
1. Take the front derailleur clamp screw off.
2. Test fit to make sure it will work in the rear derailleur (probably).
3. Take the screw to Home Depot to find a replacement.

Second alternative
1. Cruise around the neighborhood on garbage morning. Look for a trashed derailleur bike.
2. Take it home, salvage the clamp screw out of it.
3. Throw the rest of the bike away.
The last step is important because otherwise you'll trap yourself in an endless repeating loop.

Agree, except with Home Depot as being the best choice. HD usually sells small screws of this type in packaged lots, which means buying more than you need, plus may not give you the option of a physical test for match.

When I need only one or two screws, nuts or washers, I go to the local hardware store (independent, Tru-Value or Ace doesn't matter).

They have draws of hardware and will sell you one. Plus they allow trial and error matching, which opens another option, which is to remove the RD from the bike and bring it in for a screw trial and error.

BTW- the screw needed is almost certainly a 5x.8 screw, and you want stainless steel, vs. a commercial galvanized one which will rust.

Be careful if using trial and error matching a US #8-32 screw is almost identical in diameter an pitch, and will fit OK, though a bit loose. However when you tighten it, it can strip the RDs threads.

The front derailleur was not threaded like the rear derailleur so I just used a small nut and screw. I have tried fitting that screw in the rear but it does not have the right threads. I've also dug through my garage looking for both the old clamp bolt and also a new one but none of the ones I find fit.

This makes perfect sense to me but for whatever reason my neighborhood would rather let the bikes rust to the point where they flake instead of putting them on the curb for trash pickup. I'm not saying it's a bad idea at all, but if I did it, I would probably not find a singe bike.

I was thinking that Shimano would have the bolt threads listed somewhere. If I can find the threads, I can take note of it, make a trip to Home Depot, and get the right bolt. I could also take the derailleur off as well and try all the screws until I find one that fits.

Josh