Screws have gone missing

[gepabu]

Both screw which attach the mud guards to the the frame of the bike near the wheel hub have fallen out. Could someone tell what screws these are so that i can replace them? Its an audax 3 if that matters.

Thanks

[Aleman]

I would suspect that they are M5 bolts ... There is always the possibility with a Thorn ... We actually more a certainty  ... That they are actually M6.

[JohnR]

Something from this selection https://www.sjscycles.co.uk/nuts-bolts/assorted-frame-stainless-steel-fixings-approx-12-lbs-250g-bag/ should fit.

It's also worthwhile getting a little bottle of threadlocker to discourage future similar events from happening.

[PH]

I'd say almost certainly M5, but to be sure, take a screw out of your bottle cage and try that, if that fits it's M5.

[martinf]

All the mudguard mounting bolts on the 4 family Thorns are M5 stainless steel. I carry a couple of spares, along with washers and nuts, in my normal toolkit.

Checking the mudguard and rack bolts is part of the regular overhaul I do on all the bikes, the frequency of this overhaul depends on how much they are used.

[mickeg]

As noted above, some thread locker (removable, usually blue color).  If you do not have any and do not want to bother getting any, try some grease.

On my Thorns that have a tab on the fork for a bottle generator, I carry spare M5 bolts, one rack or fender type bolt and one countersunk for my bike shoe cleats.

[leftpoole]

M5. Always M5. Regular maintenance such as checking tightness should be a given. Weekly check.
I cannot imagine anyone not regularly checking all bolts on any bike.
They did not both fall out at the same time (did they?).

[PH]

Regular checking for me as well, once a year.
With the appropriate thread lock and/or spring/shakeproof washers I've never lost a screw or had one come more than a quarter turn lose.
I also have a preference to reverse a longer screw and use a nut (Usually dome) to secure the guards or rack.  This has two advantages - If the nut were to fall off the accessory could be tied onto the screw and if the screw were to shear I'd still have the head to remove it.

[PH]

On my Thorns that have a tab on the fork for a bottle generator, I carry spare M5 bolts, one rack or fender type bolt and one countersunk for my bike shoe cleats.

Good tip. likewise if you have an unused bottle mount, the screws in it might as well be those you can use elsewhere.
I think that was the thinking behind the Surly forks I have with a spare sixteen (Yes sixteen) screws in them 

[gepabu]

[Good tip. likewise if you have an unused bottle mount, the screws in it might as well be those you can use elsewhere.
I think that was the thinking behind the Surly forks I have with a spare sixteen (Yes sixteen) screws in them 
[/quote]

Thanks everyone.

Great idea. Saved me having to buy any.  I currently have two bottle holders which is excessive for me

[GamblerGORD649]

Look to see if there is room to have the bolt to stick out the inside another 6 mm. If so put a nylock nut on and never need to check if it's getting loose.

[mickeg]

The suggestion to run a bolt out from the inside for rack or fenders would have to clear the chain on the drive side.  Some bikes have those mounting points far enough away that the chain would never get near the bolt.  But your bike might have the mounting holes close enough to the chain that a bolt and chain could make contact.  It may need a pan head bolt that is extra thin.

I do not think I could run the bolt from the inside on my Sherpa, or if I could it would have to have a pan head.

My titanium bike I mounted the fenders on the inside of the dropouts and use the same bolts on the outside of the dropouts for the rack with nylock nuts.  But, that frame has the mounting points up much higher, the chain will never get near the bolts. 

First photo is looking forward towards the rear hub and dropouts on my titanium bike, you can see the fender stays are mounted on the inside of the dropouts, drive side has the stays and mounting bolt quite high above the cassette.  Second photo from the side.