What screw? Dull man’s club post.

[Milzy]

I’d like to replace this rusty screw with a better one. Any ideas on what size, thinking Bolt spec: M5x 8mm. I want high quality stainless or titanium, no more rust.

 

[PapaZita]

Nice looking frame! 😁. Pretty sure they‘re all M5. 8mm seems about the right length. A stainless button head will be nice and aero. Cap head easier to get off if somehow it does ever get stuck in there. Maybe look for a security torx if you want to confound the bike shop mechanic (or the future you).

 

[mickle]

Tres importante the replacement is not longer than the original and interfere with the bottom bracket.

 

[Marchrider]

do you think that will be a 'machine screw' or a self tapper - I don't think you will know until you remove it

i doubt ts been manufactured like that, it could have started out with a proper stainless fastener, been dismantled, then lost and then wedged a general self tapper in the hole

 

[PapaZita]

The frame will be tapped for an M5 machine screw.

 

[grldtnr]

I’d like to replace this rusty screw with a better one. Any ideas on what size, thinking Bolt spec: M5x 8mm. I want high quality stainless or titanium, no more rust.
View attachment 761307

First, you'll need to get the begger out !
A4 grade marine stainless screw , shouldn't rust, but depending on what's in there, you will likely need to run a tap in to clean the hole ,or even cut a new thread.

 

[Punkawallah]

Bi-metal corrosion is a thing.

 

[BrumJim]

Titanium will be lighter. Will save you 3s on a 5hr ride. Go for it!

 

[T4tomo]

Any ideas on what size

take it out and measure it!

 

[wafter]

Can't help with thread spec or length (the former probably common at M5 as most have stated, the latter will be relatively bike-specific I suspect). Only way to be sure is to pull it out and measure it!

I'd advise replacing with a stainless socket button cap - which will retain a similar low profile / aesthetic but with a nicer tool interface. I've replaced most of the standard fixings (for cable guide, guards, racks etc) on my bikes with these:

As @grldtnr suggests A4 is the more corrosion-resistant commercially available grade. I'd be cautious of sticking a tap up the hole - instead an old M5 bolt with a slot or three cut along its threads (like the flutes in a tap) will chase the crap out of the threads with less risk of damaging the existing threads.

GWR fasteners are my go-to for common metric bolts.

I'd probably fit the new one with anti-seize grease..

 

[Milzy]

Titanium will be lighter. Will save you 3s on a 5hr ride. Go for it!

More like 0.03 for 5 hours climbing.

 

[Marchrider]

The frame will be tapped for an M5 machine screw.

still could be a self tapper bodged in, that rusty head will not be what the bike was built with

 

[silva]

Whoever choses bolts with such heads nowadays on anything other than throw away stuff, should be used-diapered in fully.
Let alone unprotected steel, and a head sunk between a ridge so one can't put a vise on it.
Maybe an idea to first try to get it out before thinking about with what to replace.
Considering the ugly bolt choice, it's quite possible that it is way too long too, and all thread inside rusted / expanded to hell either, meaning while turning the screw it will ruin the thread in the alu tube, resulting in a hole the outer size of the bolts thread, so M5 to M6. If it's M6 next step is M8, quite a big hole that is. And screw head also bigger which will void that metal at the right side and ridge.

I would leave it, it's not worth the risk. Remove the rust from the head as much as possible (ticking, small punch small hammer, screwdriver to scratch rust off the tool inserts, blew dust/dirt off, press some sticky silicone on it, finger-strike it over to prevent dirt/water arriving within again.

 

[Marchrider]

Whoever choses bolts with such heads nowadays on anything other than throw away stuff, should be used-diapered in fully.
Let alone unprotected steel, and a head sunk between a ridge so one can't put a vise on it.
Maybe an idea to first try to get it out before thinking about with what to replace.
Considering the ugly bolt choice, it's quite possible that it is way too long too, and all thread inside rusted / expanded to hell either, meaning while turning the screw it will ruin the thread in the alu tube, resulting in a hole the outer size of the bolts thread, so M5 to M6. If it's M6 next step is M8, quite a big hole that is. And screw head also bigger which will void that metal at the right side and ridge.

I would leave it, it's not worth the risk. Remove the rust from the head as much as possible (ticking, small punch small hammer, screwdriver to scratch rust off the tool inserts, blew dust/dirt off, press some sticky silicone on it, finger-strike it over to prevent dirt/water arriving within again.

yes, unless this rusted fastener comes out easily or you have to take it out then I would leave it alone, could be a lot of pain involved replacing it for just aesthetic reasons, esp when it is somewhere you can only see when the bike is illegally turned upside down

 

[fritz katzenjammer]

I agree with the above wise types. I work in a bike shop and that particular fastener is often a nasty mess to get out. Although I’ve never seen one total seized, they usually put up a pretty good fight often causing the local plastic bits to be damaged in the process.

If lightly corroded I usually replace them before they get too mangy, but when they look like this I just give them a good coating of something oily to help minimize the advance of the inevitable. If it doesn’t need to come out leave it alone.