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From: AMuzi <am@yellowjersey.org>
Newsgroups: rec.bicycles.tech
Subject: Re: RE: Re: RE: Re: DeRosa Merak Rear Brake Problem
Date: Fri, 3 Jan 2025 10:24:20 -0600
Organization: Yellow Jersey, Ltd.
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On 1/3/2025 9:50 AM, cyclintom wrote:
> On Thu Jan 2 10:36:19 2025 AMuzi  wrote:
>> On 1/2/2025 10:08 AM, cyclintom wrote:
>>> On Thu Jan 2 09:46:17 2025 Zen Cycle  wrote:
>>>>
>>>> It's a marketing name for the piece, but not necessarily anything odd.
>>>> The "B-stay" is a Colnago proprietary seat-stay assembly of a rear
>>>> "wishbone design", except that it's a modular formed CF piece designed
>>>> to insert into a seat lug receiver and studs on the rear dropouts. IOW,
>>>> it's only a "B-stay" when it's made by Colnago. It's not a "b-stay" on a
>>>> DErosa Merak unless Derosa sourced the piece from Colnago. I believe
>>>> Columbus made a similar piece under the "Curve" moniker.
>>>>
>>>>>
>>>>> I don't recall seeing any brake mounting hardware that took an M5
>>>>> fastener. I think M6 is normal.
>>>>
>>>> M6 is normal, the issue is that tommy is still under the impression that
>>>> the screw size is defined by the drive tool, not the screw dimension
>>>> (remember his insistence that the water bottle screws on his Basso were
>>>> M4s).
>>>>
>>>> I really can't say what a "normal brake lock" is. I suspect it's just
>>>> the bolt, similar to how he called the cable clamp on the derailleur a
>>>> "lock" recently.
>>>
>>>
>>> Proprietary? This is not an uncommon assembly. Though perhaps Colnago has rights to the name. I doubt that though since Trek made on before Colnago.
>>>
>>> De Rosa Macro Aluminum Carbon Frame - Size: ST 50 TT 53 - Light Blue | eBay
>>>
>>> Canyon road bike frame Air Road CF Team Omega Pharma-Lotto Model Carbon L Rare! | eBay
>>>
>>> Giant TCR Advanced SL Medium Frameset (Trek Cervelo Specialized Colnago Merckx) | eBay
>>>
>>> Trek 120 OCLV Carbon Road Bike Frameset 58mm Large Made in USA Blue 2004 | eBay
>>>
>>>
>>
>> I did not know the term. We normally use "seatstay" or
>> "seatstays".
>>
>> For purposes of mounting a caliper, the monostay top portion
>> makes no difference. Zip. Nada. None.
>>
>> I wonder if it's "B-stay" to honor Keith Bontrager, who
>> developed and popularized that style in 1985?
>>
>> Back to your question, try slipping a 5mm bolt into those
>> threads. If it falls through, you have an M6; likely just a
>> brake allen mounting nut possibly stuck in the brake
>> mounting hole.
> 
> 
> 
> 
> Yes, it is an M6 fitting.

I thought so; that makes more sense.
It is most probably an aluminum brake mounting nut.

Possibly corroded in place, possibly stuck in with Locktite 
or epoxy, possibly just jammed into a brake mount hole 
improperly formed or full of clear coat.  Hard to say which.

It's unlikely to be a fatal problem for your frame and a new 
nut is a couple of dollars.  Observe as carefully as you can 
and do not do anything destructive until/unless you know 
what it is.

I'd try running a bolt into it, warm the area and give it a 
sharp rap. (not a full swing with a big hammer)
-- 
Andrew Muzi
am@yellowjersey.org
Open every day since 1 April, 1971