Hex keys

i bought a stainless steel

i bought a stainless steel set with ball ends. excellent. far better than normal steel ones. those seemed to mash up the bolt heads after awhile and also gradually round off there own edges. i bought mine from a standard ironmongers shop.

TypeVertigo wrote:

No real need for bike-branded hex keys to be honest. Bondhus or Stanley should be enough methinks – they’re plenty accurate as they are, and should last a while. Perhaps I wouldn’t recommend going too cheap, but Bondhus and Stanley are a good place to start.

Got to agree, I’ve been using CK ones and they are fine and not had any rounding.  Forgot how much they cost but must have been less than a tenner. 

guyrwood wrote:

That’s a very good point and I strongly suspect you are right. Having said that, at least if you know your keys are dimensionally accurate you’ve got the best bet of them fitting well. Ie. If the distribution of actual socket sizes is on a bell curve (ie a few too tight, a lot more or less right, some perfect or close, a lot very slightly too big and a few too big) you have the best chance of getting a good fit and the lowest chance of rounding out a bolt head.

You’re getting there.

What happens is that there will be an ISO standard which will specify to what
tolerances hex bolts should be manufactured to. It may also indicate how high
you can torque them too. If you need a higher torque, use a bigger hex bolt or
different fastener altogether.

That standard may reference other standards such as the one for threads which specifies the pitch and lead of “standard” threads.

The factory that knocks out so many millions of hex bolts (made out of a
material that is itself standardised), will carefully control the manufacturing process to produce bolts within spec.

They will have some geezer at the end of the line doing QA (quality assurance) who will pull out every nth bolt and measure it. He will of course have to account for how accurate his measuring instruments are. His micrometer or whatever will be calibrated to give a reading that is plus or minus whatever at some temperature.

He records his measurements and then puts his stats to work. By wielding
mathematics, even though you’ve only measured a tiny fraction of the bolts,
you can determine whether any are out of spec.

Then you come to the manufacturer of hex keys. The mech/man engineer in charge
of making them will read the ISO standard for hex bolts and the ISO standard
for [i]”Limits & Fits”[/i] and then establish what is the acceptable range of
widths he needs to make the keys to. He will use the same methods as the bolt
manufacturer uses, alluded to above, to insure this.

In theory, given a bolt with the largest possible socket in it’s head (within
spec), you should be able to torque it up with a key with the smallest
possible width (within spec) without rounding out the bolt socket or rounding
off the key.

In practice, YMMV. I rounded out a hex bolt on a stem once. I suspect the material the bolt was manufactured from was not man enough for the job rather than the fit between key and bolt was too loose.

Personally, I use cheap hex keys: Lifeline from Wiggle I think. On the
principle that it’s pretty difficult to bugger up manufacturing a hex key and
they tend to get lost anyway.

You can’t go wrong with

You can’t go wrong with Halfords Advanced Professional tools. Lifetime warranty and usually cheaper than the “bike-specific” (it really isn’t) equivalent.

Get some decent ball-end allen keys and, if the bolt rounds out, it’s a crap bolt.

What you post makes sense. 

What you post makes sense.  However, my experience says that expensive ones actually do fit better, and that chart on BikeRadar backs this up – all the cheap ones are undersize.

I suppose if you are going to use sloppy manufacturing tolerances, making them undersize is wise because they will at least fit in the bolt head, unlike wildly oversize ones.