ISO: M5x.8 20mm Hex Socket Bolt with <8.0mm head diameter

[ColonelJLloyd]

I need to install a post mount disc caliper on a flat mount carbon fork, so I need to use an adapter, which I have in hand (I know it's ugly, but I need to be able to easily switch between a steel ISO tab fork and this carbon one). The adapter mounts to the fork with two M5x.8 bolts. Length can be variable, but 20mm looks like the best bet with plenty of purchase.

While while a run-of-the-mill bolt will fit inside the adapter, the diameter of the bolt head makes it exit the adapter at an angle that is not 90 degrees; no good. Most of the socket head M5 bolts I have here have a head diameter of about 8.4mm. I have one M5x20mm bolt that has a smooth socket head that measures ~7.9mm and it works well. I need another. Anyone know of a source for these? I'd rather not order 100 from McMaster Carr, the big box stores will almost certainly only have the knurled head ones that measure <8mm and the last local Ace that had a proper hardware selection shut their doors a few years back.

I don't think it's entirely attributable to my poor Google-fu, because I don't think most sellers list the diameter of the bolt head. Any help is appreciated.

I considered reaming the recess of the adapter, but this isn't my preference.

[kramnnim]

Can you just grind it down to 7.9mm? Put the threaded end in a drill and spin it against a file or sandpaper like a makeshift mini lathe.

[donevwil]

My bet is that the "smooth" headed SHC of yours is actually a 10-32, not M5.

[ColonelJLloyd]

Can you just grind it down to 7.9mm? Put the threaded end in a drill and spin it against a file or sandpaper like a makeshift mini lathe.

Yeah, manually reducing the diameter to fit is my backup.

[oliver1850]

8.4 mm +/- .1 mm is the spec, so I doubt you will find one from a hardware retailer.

I can easily turn one down on the lathe. I will have to check and see if I have one on hand that is 20 mm long.

[ColonelJLloyd]

My bet is that the "smooth" headed SHC of yours is actually a 10-32, not M5.

Good point. It's possible as I don't remember actually threading it in the fork when I was messing with this last week. I will check this. It begs the question why this adapter (https://www.chainreactioncycles.com/us/en/clarks-anodised-mount-adaptor-flat-to-post/rp-prod179773), which did not come with hardware, would require this somewhat non-standard bolt. Further, shouldn't I really be using a washer under the head? I certainly don't have an M5 washer with a diameter that small. Maybe the best answer is to chuck this in the trash and get a different brand adapter.

Another head scratcher was why the adapter came with two of these shims. I wasn't even sure what they were, but some searching shows that Jagwire sells them as 6-bolt rotor shims. I guess they are intended to use on one side of the adapter to ever-so-slightly tilt the caliper inboard or outboard if needed?

https://live.staticflickr.com/65535/48234725236_756b52b992_c.jpg (https://flic.kr/p/2gukzkJ)Untitled (https://flic.kr/p/2gukzkJ) by ColonelJLloyd (https://www.flickr.com/photos/51002114@N03/), on Flickr

[oliver1850]

My bet is that the "smooth" headed SHC of yours is actually a 10-32, not M5.

I think you are right. Spec head diameter for 10-32 is .312" (7.925 mm).

I have used 10-32 to substitute for M5 before with no trouble, but #10 is about .1 mm smaller in diameter from M5.

[donevwil]

...I have used 10-32 to substitute for M5 before with no trouble, but #10 is about .1 mm smaller in diameter from M5.

Same here for rack or fender mounting, not for a brake adapter.

[ColonelJLloyd]

Same here for rack or fender mounting, not for a brake adapter.

Haha. I'm with ya. Not worth the risk of failure or voiding the fork warranty in this application.

This KCNC one comes with hardware and, as closely as I've looked at M5 bolts recently, those do look like a slightly smaller diameter head than your normal M5 bolt. And the bolts have integrated washers which would make me feel a lot better.

https://cdn10.bigcommerce.com/s-tqfdy/product_images/attribute_rule_images/13338_thumb_1484947526.jpg

[scoobydrew]

If you're still keen on buying an off the shelf solution, browse through the Misumi site as they offer a couple different varieties of smaller than standard socket head cap screws. Check out part number CSHSM-SUS-M5-20 as an example.

[Dino Suegiù]

I need to install a post mount disc caliper on a flat mount carbon fork, so I need to use an adapter, which I have in hand (I know it's ugly, but I need to be able to easily switch between a steel ISO tab fork and this carbon one). The adapter mounts to the fork with two M5x.8 bolts. Length can be variable, but 20mm looks like the best bet with plenty of purchase.

While while a run-of-the-mill bolt will fit inside the adapter, the diameter of the bolt head makes it exit the adapter at an angle that is not 90 degrees; no good. Most of the socket head M5 bolts I have here have a head diameter of about 8.4mm. I have one M5x20mm bolt that has a smooth socket head that measures ~7.9mm and it works well. I need another. Anyone know of a source for these? I'd rather not order 100 from McMaster Carr, the big box stores will almost certainly only have the knurled head ones that measure <8mm and the last local Ace that had a proper hardware selection shut their doors a few years back.

I don't think it's entirely attributable to my poor Google-fu, because I don't think most sellers list the diameter of the bolt head. Any help is appreciated.

I considered reaming the recess of the adapter, but this isn't my preference.
The head on your M5 bolt is probably 8.5mm diameter, standard.

Toronto Cycles sell beautiful titanium M5 "Narrow Head" bolts, with a head measuring 7.5mm in diameter.

About 3/4 of the way down, left side, of this funky web page:
http://www.torontocycles.com/Selling/Titanium_Bolts.html

Titanium Narrow Head Bolts
5mm Titanium Narrow Head Bolts
This bolt has a narrower head than standard bolts.
Head Diameter = 7.5mm (Standard is 8.5mm)
4mm Hex Socket, 5mm bolt.
M5x40 Narrow Head
$3.50
http://www.torontocycles.com/sitebuilder/images/Titanium_Bolt-186x192.jpg


They sell matching washers, etc. too.

Only sold in 40mm lengths but you can cut down to your spec.
At $3.50, buy some other things too, because iirc the minimum shipping charge is $7 to USA (no tracking, with tracking much more).

TC is an excellent store, great service.
There is at least one other small order specialty bolt store online that would likely also have these, but I don't remember the name right now. Somebody else will. But TC is really good, the owner is super.

[ColonelJLloyd]

TC is an excellent store, great service.

And an ordering platform one step away from complete garbage (the water bottle bolts I want don't have a "buy" button or a part number). Ha. This is a great recommendation, though, and one I had forgotten about. I've ordered from them once before.

I measured the depth of the threading on the fork mount and they are not as deep as I thought so I do need to go with a 15mm bolt. I'm also not really excited about cutting titanium bolts with a hacksaw or cut-off disc, but no need as I kept looking around the site and they sell a narrow head M5x15 with washer and a T25 socket which will would work out great. The M6 caliper mounting bolts I have are Ti and T25 so it would make good sense.

Oy. I think I'm just going to email him with what I need and have him send me an invoice as this site is wearing me out.

Thanks to everyone for the responses and feedback; very helpful.

[Dino Suegiù]

And an ordering platform one step away from complete garbage (the water bottle bolts I want don't have a "buy" button or a part number). Ha. This is a great recommendation, though, and one I had forgotten about. I've ordered from them once before.

I measured the depth of the threading on the fork mount and they are not as deep as I thought so I do need to go with a 15mm bolt. I'm also not really excited about cutting titanium bolts with a hacksaw or cut-off disc, but no need as I kept looking around the site and they sell a narrow head M5x15 with washer and a T25 socket which will would work out great. The M6 caliper mounting bolts I have are Ti and T25 so it would make good sense.

Oy. I think I'm just going to email him with what I need and have him send me an invoice as this site is wearing me out.

Thanks to everyone for the responses and feedback; very helpful.
Well, I did write that the site is "funky". ;)

And I apologize for not mentioning the ordering bizarreness, with the whole separate PayPal page that pops up. Not only that, the site doesn't remember your cart if you open up a separate webpage even at the same time, Etc. So weird and just a complete headache.

So, I do exactly what you wrote: compile a very specific list of the items I want, email it to him, and write, "Tom, please send me an invoice for this order." He is very prompt at replying, and the shipping has always been quite fast too.

He seems to be very old-school though, so my order form to him is a Word or Excel table, really complete, with:

Columns:
PART NUMBER/PART DESCRIPTION/COLOR (IF APPLIES)/SMALL PHOTO/PRICE PER UNIT/QUANTITY/TOTAL PRICE

Rows:
1
2
3
4
ETC

SUBTOTAL
SHIPPING (he fills this in)
TOTAL

This makes it easy for him, and makes me feel more secure. Better safe than sorry.
He has never erred once with that system.

I'm happy that you found what you need.

PS: In a pinch, I have cut ti bolts with a 32tpi blade and then finished the ends with a fine file. They engage and work perfectly fine as long as you don't cross-cut the threads.