socket cap bolts

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mumbojumbo
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Joined: 1 Aug 2018, 8:18pm

socket cap bolts

Post by mumbojumbo »

I wish to purchase some bolts to attach mudguards ,bottle cages and racks.Two questions

1.which size do I need ?
2.what length will secure a rack and guards?

Thanks
Jdsk
Posts: 24636
Joined: 5 Mar 2019, 5:42pm

Re: socket cap bolts

Post by Jdsk »

They're often M5. Bottle cage bolts sometimes 15 or 20mm long.

Jonathan

... and similar for bottle cage screws. : - )
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fausto99
Posts: 952
Joined: 19 Sep 2011, 10:06am
Location: NW Kent

Re: socket cap bolts

Post by fausto99 »

Socket head is ok. Just don’t buy button head Allen screws. The tiny hex will round out before you can get them tight enough.
colin54
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Joined: 24 Sep 2013, 4:34pm

Re: socket cap bolts

Post by colin54 »

mumbojumbo wrote: 21 Oct 2021, 5:58pm
2.what length will secure a rack and guards?

Thanks
Are you talking about securing rack and guard sharing one braze-on per side or two separate ones ?
I just bought some the other day
Bottle cages M5x 12
Mudguards M5x15
Guards sharing a braze on M5x20
Some washers and M5 nylocs are handy as well for a through bolt in case a thread strips.
I bought some M5x 25 for rack top screws, just in case the above was too short - handy to cut down as well. I put a nyloc on the back on the non-drive side if they are sharing a braze-on, there's not enough room for a nut on the drive side (fouls cassette usually). I've had to tap out shared ones before to M6 due to stripped threads, but really you are better of securing the guard to the rack stays using rubber coated P-Clips of similar in the first place if you only have one braze-on.
I got the last lot from Bolt Base , on ebay or from their site
https://boltbase.com/
Bikes such as Spa use M6 for the racks
Last edited by colin54 on 21 Oct 2021, 8:54pm, edited 1 time in total.
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rogerzilla
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Joined: 9 Jun 2008, 8:06pm

Re: socket cap bolts

Post by rogerzilla »

M5 on anything recent. 2BA on older British bikes.
axel_knutt
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Re: socket cap bolts

Post by axel_knutt »

fausto99 wrote: 21 Oct 2021, 7:22pm Socket head is ok. Just don’t buy button head Allen screws. The tiny hex will round out before you can get them tight enough.
I've got button heads on mine, just because I prefer the look of them, and they're big enough not to need a washer. I've not had any round off, or come undone.
“I'm not upset that you lied to me, I'm upset that from now on I can't believe you.”
― Friedrich Nietzsche
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andrew_s
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Joined: 7 Jan 2007, 9:29pm
Location: Gloucestershire

Re: socket cap bolts

Post by andrew_s »

M5 is normal, but a few bikes these days have M6 rack braze-ons. Bottle cage bolts are M5, so borrow one to check whether it screws in properly.
Length is 15 mm for an aluminium rack, 2 washers, and a double stay.
If your mudguards have two separate stays each side, each with their own loop, you'll want 20 mm.
I agree than they should take a 4 mm allen key. 3 mm sockets are too small and will round out easily.

On a touring bike, I'd generally make a point of replacing a couple of the bottle cage bolts by longer ones, suitable for a rack or anything else that may lose or break a bolt, so I've a ready spare in case of need.
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fausto99
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Joined: 19 Sep 2011, 10:06am
Location: NW Kent

Re: socket cap bolts

Post by fausto99 »

axel_knutt wrote: 22 Oct 2021, 12:32am
fausto99 wrote: 21 Oct 2021, 7:22pm Socket head is ok. Just don’t buy button head Allen screws. The tiny hex will round out before you can get them tight enough.
I've got button heads on mine, just because I prefer the look of them, and they're big enough not to need a washer. I've not had any round off, or come undone.
I liked the look of them too. That's why I bought them, but on a lejog I only got to the Scottish border before they rounded out and had to be replaced. Mine were stainless steel. Maybe non ss would be OK, but it is a very small hex and luggage racks need to be on tight...
Jdsk
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Joined: 5 Mar 2019, 5:42pm

Re: socket cap bolts

Post by Jdsk »

andrew_s wrote: 22 Oct 2021, 12:37amOn a touring bike, I'd generally make a point of replacing a couple of the bottle cage bolts by longer ones, suitable for a rack or anything else that may lose or break a bolt, so I've a ready spare in case of need.
Wise words.

And before setting off on a tour I go over the bikes and as well as inspecting and tightening the bolts I check for consistency and spares for each type.

Jonathan
boblo
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Joined: 24 Sep 2009, 7:35pm

Re: socket cap bolts

Post by boblo »

On tour, I usually take a few spare m5's/washers/nuts. They have a habit of working loose and falling out and you usually find out when it all starts rattling despite daily checks...

I also find button head a bit soft so stick with cap head for anything that needs to be 'tight'. It can depend on the quality/fit of your keys but I don't usually take Wera etc on tour...
nsew
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Joined: 14 Dec 2017, 12:38pm

Re: socket cap bolts

Post by nsew »

boblo wrote: 22 Oct 2021, 9:30am On tour, I usually take a few spare m5's/washers/nuts. They have a habit of working loose and falling out and you usually find out when it all starts rattling despite daily checks...
In that case the receiving thread is becoming increasingly sloppy and weak each time the bolts work loose. Can you re-tap to M6?
slowster
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Re: socket cap bolts

Post by slowster »

Button head bolts are often better for bottle cage bosses, because the protruding head of a socket head will often rub against the bottle (and similarly interfere with using a frame fit pump against the seat tube if the bolts are simply blanking the boss).

With regard to the limited amount of torque that the smaller allen key permits with button heads and the risk of rounding out, I think that where it is possible to do so with rack and mudguard eyelets, it's better to insert the bolt from the other side of the eyelet and use a Nyloc nut to secure the rack/mudguard stay. The Nyloc nut takes the stresses, and the bolt then does not need much torque and is probably unlikely to loosen, especially if threadlocked. It then probably makes little difference whether the bolt is a button head or socket head.
keyboardmonkey
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Joined: 1 Dec 2009, 5:05pm
Location: Yorkshire

Re: socket cap bolts

Post by keyboardmonkey »

mumbojumbo wrote: 21 Oct 2021, 5:58pm I wish to purchase some bolts to attach mudguards ,bottle cages and racks.Two questions

1.which size do I need ?
2.what length will secure a rack and guards?

Thanks
M6
M6
These bolts (screws?) fastening the front mudguard stays were on the pre-loved bike I bought recently. Naturally, I was freaked out that they didn’t match :shock: and were too long. I was surprised that they were M6, so I measured how long I needed them to be and bought suitable replacements online.

When I fitted new mudguards I was again surprised that the combined rear mudguard/carrier eyes took an M5 bolt/screw (cue more :shock:)

Anyway, to otherwise standardise and tidy up the other socket caps I bought these from a well-known online retailer:

M5
M5
The longest are far too long, but since I needed some for cutting down to custom lengths I reckoned it didn’t matter by how much they were too big.

Then I spread some of them out in to my small parts container (a repurposed fishing lure box).

Lure box
Lure box
Lure box with SKS chainstay bridge brackets
Lure box with SKS chainstay bridge brackets
Be careful. It’s a rabbit hole you might be lured in to...
Last edited by keyboardmonkey on 9 Feb 2023, 6:09pm, edited 1 time in total.
Jdsk
Posts: 24636
Joined: 5 Mar 2019, 5:42pm

Re: socket cap bolts

Post by Jdsk »

If anyone is unfamiliar with cutting *bolts to length... I suggest running a nut up first so that when it is removed it reforms the thread where there might be damage from the blade.

Jonathan

* Or screws. : - )
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