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so recently I have been having problems with my bike: the wheels tended to slip out of the dropout and rub against the frame of the bike. However, I had found a way to fix (reorient) the wheel everytime it did so. Atleast I thought I did. I would loosen this screw and the bolt next to it (to be able to reorient the wheel) and then fix the orientation. However, this problem kept persisting every time I rode. Once when I was reorienting, I unscrewed the screw a little too much causing what it was holding (a metal washer like thing that I assume helped the wheel stay in place) on the other side of the dropout to come loose and fall out. The screw that I had the accident with is below marked by the red rectangleenter image description here

How do I fix this?

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    The screw and the gizmo behind it fit into the slot in the dropout, and serve to keep the derailer hanger from twisting on the axle. Assuming you haven't lost the parts you fix it by simply putting it back together. The gizmo will usually have a curve on one edge that is designed to fit the "dead end" of the dropout.
    – Daniel R Hicks
    Commented Apr 3, 2021 at 23:59
  • @DanielRHicks That's the answer.
    – Criggie ♦
    Commented Apr 4, 2021 at 4:28
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    It's an evolutionary vestige from the times when bikes had not yet grown a derailleur hanger at the right dropout. If you've lost bits, don't despair, they are still available, even as NOS, especially in older bikeshops or on auction sites.
    – Carel
    Commented Apr 4, 2021 at 7:13
  • I have not lost the parts. But how do I put the "gizmo" back into the dropout? Do I need to take the entire wheel out?
    – Legend ile
    Commented Apr 4, 2021 at 16:36
  • @Carel Looks like my neighbor’s bike hasn’t reached puberty yet then. It doesn’t have the typical adolescent disc brake mounts yet.
    – MaplePanda
    Commented Apr 4, 2021 at 18:27

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The derailleur you are using has an integrated adapter claw. A rear derailleur hangar claw. The bolt you have circled is used with a special washer to properly orient and secure the claw, which puts the derailleur in necessary position and alignment to the cogs for good shifting. This bolt has little to do with the axle alignment of the wheel and once it is in correct position with it's special washer/nut and secured, it shouldn't be loosened. Occasional inspection and possibly re-torquing the bolt to an appropriate tightness is all that is necessary after install.

Typically with a claw hangar the special washer/nut has a rounded side which has a lip of metal around it's radius. The rounded end fits into the rounded end of the frame's right rear drop out--this helps position the claw hangar correctly. The lip around the perimeter, sits on the inside of the drop out, following the arched perimeter of the end of the dropout. Tightening the bolt into the washer/nut brings this lip tight to the inside of the dropout and acts to secure the claw hangar to the frame.

When you want to adjust the wheel, you need only loosen the larger axle fixing nut. Loosen both the right and left axle nuts, center the wheel fully in the drop-outs. The axle will be touching the claw's fixing washer/nut on the right. The left axle may have a bit of gap between the closed end of the dropout and the axle. This may be necessary for proper wheel alignment and centering. Tightening the axle nuts up again, go back and forth, right to left, more or less tightening the nuts up together. This preserves the centering of the wheel since one side is not becoming overly tight compared to the other side which can cause deflection of the wheel in the dropouts.

For clarity, I've included a photo of a universal derailleur hangar with the same fixing system as your integrated claw hangar. This highlights the specially shaped nut which sits in the end of the dropout. The hangar is then fixed in correct position by the clamping force of the lip at the inside and body of the hangar outside as they are drawn together by the tightening bolt. derailleur hangar fixing system derailleur hangar and fixing bolt/nut

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  • Ok. So how would I go about putting the washer back into the screw and dropout?
    – Legend ile
    Commented Apr 5, 2021 at 18:19
  • @Legendile not sure where your washer is - the photos above show a generic hanger, and all I can imagine is a former owner adding a washer. Try assembling yours as per the photo and see how it fits your frame. If something seems wrong, take a photo and add it to the question with edit
    – Criggie ♦
    Commented Apr 5, 2021 at 19:35
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    @Legendile In my photo that nut is a single piece. It would be placed in position in the dropout from the inside (the rear wheel off would be helpful here). The arched aspect fits in the dropout while the lip around it remains on the inside around the perimeter of the dropout. The hangar body remains outside the frame (at the dropout) and the hangar fixing bolt goes thru it, the frame @ dropout, then threads into the special nut which is in position in the dropout.
    – Jeff
    Commented Apr 5, 2021 at 20:09

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