installing fenders on my 1990's mountain bike, all the mounts are there. front one went fine. back one, I guess the thread was messed up. long story short I broke the screw off in the mounting hole flush to the metal

have been trying to not go to the bike shop and do things myself.

Advice needed on how you would extract the remaining part of the screw and then fix the threads so the fender can be mounted

I'm no handy man and don't have a ton of tools, but do have a good drill, wrenches, etc.

​​​​​​​thanks

can you post a pic? Drilling the screw out or using an easy out and then tapping the hole is what is probably required.

From a machinist's point of view, here's what I'd do. Get a center punch (they're only a couple of bucks) and carefully center-punch the screw. This will produce a small divot that will keep the twist-drill ("bits" are for wood working) from "walking". Next buy the proper-sized twist-drill and ez out--again, only a few bucks. Then drill and ez out the screw. Patience and penetrating oil are your friends. Then buy the proper tap-again only a few bucks- and re-tap the hole. You should be able to fix it for less than $15. You'll have a few new tools for your tool box and the satisfaction of having done it yourself.
Please keep us posted on the out come.
Jon

left hand drill bit

A fender mount screw isn't very big so that would be my thought too. Then, if I had the right tap, I'd chase out the hole. If I didn't have the right tap I'd gingerly test a longer screw to see if I could get it to run all the way through (my bet is that it will). If it binds up very much it's back to the tool store for the tap.

I've told myself many times that I really need a set of these. Thanks for the reminder.

I questioned this when I first read it, but then consulted my copy of Colvin's Machinist Dictionary to review the 15 pages devoted to drills, His definition for "Wood Drill" began: "Drills for boring holes in wood; usually called 'bits'." I am now enlightened, though I wonder what I should call a twist drill that I use for wood.

what tap would he need? M5 x 0.5 Metric HSS Right Hand Thread Tap?

regardless, my suggestion is, if you use a tap, use a proper tap wrench with it. not locking pliers to turn it. I have something like this Vermont American 21916 T-Handle Tap Wrench 0 through 1/4 Inch

I have used left hand drill bits like these. you might want more than one in case you break one or it gets dull Century Drill and Tool 74108 Left Hand Stub Drill Bit, 1/8-inch

here are some others I've used Irwin Tools 30508 1/8-Inch Cobalt 135-Degree, Left Handed-Mechanics Length, Pack of 6

for normal drill bits I like these DEWALT DW1361 Titanium Pilot Point Drill Bit Set, 21-Piece

for screw extractors, I didn't have luck with the easy-out type. they do work for some ppl but I settled on straight fluted extractors like this Williams EX-21A 1/8-Inch Fluted Screw Extractor

my project was on a slightly larger bolt whose head I broke off in my Subaru. drilled a hole in the bolt, then proceeded to break a hardened steel easy out in the bolt probably cuz I used locking pliers to turn it not a proper tap wrench, so then I had to drill into that hardened steel tool, inside the bolt. in order to get a proper hole for the extractor. so don't be like me, don't break a hardened steel tool in the hole that you drill!

take your time, be patient, don't rush, use the right tools, where eye protection, don't give up, my project spanned several weeks, but I got it because I made sure the hole was deep enough & the correct diameter for the extraction tool







sometimes a left hand bit is all you need

From my experience removing broken hardened steel tools like taps and ezy outs, it is often easier to use a punch and fracture the tool and pick out the pieces with a pick/magnet than to drill it out. M5 might not be so easy due to the small diameter.

this is like the 3rd or 4th post on similar topic the past few months. we should have a sticky thread for stuck/broken bolts so ppl can always know where to go for the same advice over & over again

A picture would really help. If it;s just in the tab, drill it out completely and use a nut on the back side. I work at a bike shop part time and do this all the time.

you can fuhgeddaboudit & substitute a small compression clamp like they use on bikes without the screw holes. every hardware store carries them. this way you can ride your bike while you figure out what you want to do about the broken bolt



you can also make your own out of metal strapping

On a bike frame you won't need an easy-out or reverse drill because the grub will come out the other side... Just go very slowly with a drill bit 2mm smaller than the thread (3mm in a 5mm thread or 4mm in a 6mm thread as i expect it is), and when the drill bit bites into the grub it will turn it out the back of the thread. You may have to remove the rear wheel or whatever to allow for this.

some good advice here. Am working up the courage to solve this and will update. thanks for the responses

Just remember LH drill bits need to rotate counter-clockwise if you try that.

And be sure to chuck the smooth end of the bit in the drill,

and use the fluted end to drill with.

You can buy extractor kits that include the counter clock-wise drill bit. I don't think I've ever had to use the extractor. The LH drill bit always starts backing out the bolt before I'm done drilling it. Counter-punch it first.

An auger, or a bit.
Jon

This is not a given. It may or it may not. Plan for a worst-case scenario and hopefully you'll be pleasantly pleased.
Jon

"Center" punch, not "counter" punch.
Jon

couple of things. the screw was going in crooked when it broke. after trying to get the screw started many times, I pretty much forced it into the hole, mistake

not sure how to resize the pic, sorry for that

thanks again

here is a pic. I use the trainer to hold the bike

the blue stuff on the thread was on the screw out of the package

Harbor Freight sells a low cost set of LH drill bits. I'd do like suggested earlier and center punch the broken screw and then start drilling. Use the smallest bit and then work up in size one step at a time. It's extremely critical to stay centered in the screw you are drilling. If you are not centered work the bit sideways until you are. As the screw becomes a shell so to speak it will most likely spin out. And whatever you do don't use an ez-out. They are extremely easy to break off unless you are familiar with them, and once broken off you are going to be in a world of hurt.

here is an update. I attached that side of the fender with a couple of zip ties and am going to try it out, it looks like it might work. still will extract the screw but can ride for now. will snap a pic soon

Ha, counter-punch. Don't know where that came from...

Pro tip - grind or file the broken off stub flat if you plan on drilling it. Might also want to heat it up if it had the thread locking compound on it.