I have a couple of older bikes that have more hex nuts and Phillips/flathead head screws than Allen head bolts. These are from the early 1980s and earlier.

Little by little, I am replacing all the hex bolts and the screws with Allen head bolts. I'm not being all scorched-earth about it, but when I work on a job that involves loosening a hex nut or a larger screw, I root around my bits bin for the appropriate 6mm, 8mm or 10mm Allen bolt to replace it.

Eventually, I hope to be able to banish the hex wrenches from my carry-along toolkits, thus saving, oh, about 40 grams. I just need to find a solution for holding the hex nuts.

[I'm feeling my own forehead as I read this - I must have a sickness.]

I do the same, hex socket cap screws in stainless. Don't forget to grease the threads. You will only need a few hex wrenches. For the nuts, just carry only the wrenches you need, there will only be a couple. Hint: open end and ignition wrenches generally have two sizes per wrench, cutting down the number needed if thoughtfully selected.

JYL- I do the same thing. It is a sickness.

If you're shopping for unusual sizes of metric stainless hex bolts, Winks in downtown Portland has an excellent selection. If you're out east, I get a lot of mine from Parkrose Hardware.

I think it is a great idea and every bolt would end up being a 5 allen wrench

Are you touring? I seldom have issues with things coming loose on two there hour ride and often just ride with a tubular and CO2

Bianchigirll- I hope some of your bolts are other then 5mm headed. Some need greater torque the a 5mm allen wrench can give, others far less. But i do understand your goal. Ever hear of Alex Pong and Magic Motorcycle? Andy.

Acutally I was wrong it is a 4mm Allen. Bottlecage, rack, .......some derailleur cable bolts. Unless I am hauling super heavy panniers what needs so much torque? I did think the OP was refering to his cranks when he was talking about replacing bolts.

I am replacing the little common bolts with Allen heads, not bigger stuff like crank bolts or specialized stuff like brake through bolts. I figure the odds of having to pull a crank with just one's carry-along 200 gram tool kit are not high. Though the self extracting crank bolt set you linked to, in the other thread, are mighty interesting.

Disease has a next step, to Titanium Bolts..

I saw a British Company making Ti, unique rather than Hex socket bolts ,
to resist getting your bike stripped, using a technology like the security bolts
to retain your Custom Wheels on your car.

kind of like string theory , there are lots of non regular shapes..

https://atomic22.com/

Wasn't there a Shimano groupset where as many functions as possible were peformed using a 5mm allen key? I seem to remember seeing something on Sheldon's site about it.

I have occasionally thought about Ti bolts. My Cannondale is down to 17.8 lb and I'd be curious if I could get it to sub-17, without going to modern carbon fiber components. Ti bolts seem like the last resort though. Seems like drillium would come first. Reasoning being that replacing a given volume of steel with titanium would save less weight than replacing the same volume of aluminium with air.

Hmm, I just calculated that drilling 53 holes in the big chainring and 39 in the little chainring should save around 1.5 ounce. Gotta recheck that at home. EDIT: no, I'm wrong, that estimate is about 2X too high.

Ti bolts are considerably weaker than steel bolts. Carrying around the extra weight of the steel bolts will slow you down a lot less than having the face-plate of your stem snap off on a downhill.

Recommend the Dewalt hex wrench set as being very tough and fits into a tool kit easily. I think it is about $15 at a Home-Depot.

Mavic while they were trying to be a Pro level full component company,
used allen head capscrews.

Been there, done that, have the t-shirt.

A touring/commuting bike should have as many fasteners as possible in 5mm, but on a race bike it's much nicer if everything's fully optimised... and if everything's allen, you've got 8,10 or even 12mm down to 2 or 3.5 mm anyway.