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I couldn't comprehend, why this ring is needed. Please refer the pictures. Its a road bike (I am not sure if it matters or not, so felt like mentioning it).

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In my Bicycle, this ring usually comes out loose, Should I be worried and get it replaced?

Edit: Its an old bike, I have myself rode on this one for nearly a 3K miles so far, since I bought it from a person who had been using it. The model might go down to be roughly 7-8 years old. Nonetheless, I love this one.

P.S.: Pardon me for poor quality of the images.

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    That's a "lock ring". It's supposed to be threaded tightly onto the "cup" in the center and against the edge of the "bottom bracket" behind it so that it keeps the "cup" from screwing in or out. The "cup" is what adjusts how tight the bearings are. If the "lock ring" is loose then likely the "cup" is loose and the crank bearings are loose as well. This needs to be attended to by a knowledgeable person. – Daniel R Hicks Nov 19 '15 at 13:16
  • (The bike appears to be in good shape for being at least 40 years old.) – Daniel R Hicks Nov 19 '15 at 13:18
  • It may be an older bike, or it may be a newer low end bike. I've seen what I thought were antiquated parts on brand new bikes. I think they use parts of older design to make sure they aren't infringing on patents. – Kibbee Nov 19 '15 at 14:08
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    @Kibbee - The thing I noticed is the cottered crank. But I failed to notice that it's not a derailleur bike -- either single speed or 3-speed hub, I'd guess. Cottered cranks did hang around on non-derailleur bikes for awhile (though I'd be truly surprised if any are still manufactured). – Daniel R Hicks Nov 19 '15 at 15:00
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    Possible duplicate of Lock ring won't reattach on bottom bracket – Móż Nov 19 '15 at 20:02
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You have an older pre-cartridge bottom bracket. The bottom bracket is the axle and bearing assembly for the crankset. Rather than sealed bearings it has either loose ball or caged bearings. While the bottom bracket is assembled the cup is adjusted to the correct preload. Preload determines how much movement there is between the bearings and the axle. It should be adjusted so there is a minimum free-play but still spins freely. Once the adjustment is made the ring is tightened to hold the adjustable cup in the correct position.

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    If the ring had been loose for a longer time the bottom bracket may be in bad need of adjustment or even overhaul/replacement depending on the damage it may already have suffered. It's quite a fiddly operation and you better take the bike to a shop if you're not acquainted with the procedure or don't have the right tools. – Carel Nov 19 '15 at 16:13
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It's part of the bottom bracket but it shouldn't be loose. I'd guess you have an older style cartridge BB but again, I don't think it should be loose. It could indicate that the bearings are going to be open to the elements. If you're concerned i would take it to a bike mechanic to have it looked at

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