What is this Stay adjustment tab?

[GeorgeET]

This is on a 1985 Fuji del Rey. Bike works fine. However I am puzzled by this Phillips screwed in tab on the right derailleur side that stops the axle from going further back. The left hand photo shows the gap in the axle stays. Looks like the wheel can move back and the brake pads may would need lowering.

[RobAR]

Hey George. Forgive me. I thought that you were an 'old fart' like me!
Your Fuji frame was made during a transitional period when 'direct mount' rear drlrs, like yours, were just coming on the scene. You have Horizontal dropouts as opposed to Vertical. Most modern bikes employ Vertical as wheel removal is easier and also eliminates your part in question.
For the life of me, I can't remember what they are called.
Their purpose was to center the axle Left to Right so that the wheel sat true. Your Fuji is missing the Left side part. Both sides should have one.
The advent of Quick Release hubs, like yours, is what prompted this little part. Vertical dropouts and tighter tolerances on frame jigs eliminated that part. Any LBS that has been around for some time probably has a few in a parts bin, even if the young mechanic has no clue what it is. Try asking for a "10 spd Banjo". Banjo's are often used on BMX bikes to fine-tune chain tension.

Without the part in the left dropout, your wheel may have a tendency to let the axle move rearward on that side under hard torque.

Another alternative is to remove that part so that both sides of the axle rest in the rear-most part of the dropout. You will increase the wheelbase by, maybe, 1/2". Make sense?

[GeorgeET]

Thanks for the answer RB.Whats this about you being an old fart? If you are than I must be too:-))

Did not know both sides had one, this is how I got the bike. I'll bug my LBD again for weird old parts. Ye they have slide out tabs so I can see how they can be used to set center.

It works fine this way and stays centered fine.I may fool around and remove it and move the wheel back if I do not have to mess with the brakes too much and its centered. The wheelbase will be a bit longer and slower handling but thats OK.

I thought it had something to do with deraileur angle, or converting the bike from a racer to a tourer by changing wheelbase length.

Ye I looked at some fixie info and it said that horizontal drop outs were needed. BTW I find myself riding in one gear like a fixie 42T X 14T on my ride by the beach this Sunday. Seventy degrees and sunny, lots of babes on the beach and bike path, Nice.